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Lesmahagow High School Structure Bonding & Properties

Lesmahagow High SchoolNational 4/5 Chemistry

Chemical Changes & Structure: Structure, Bonding & Properties

Through gaining an understanding of the structure of atoms and how they join, I can begin to connect the properties of substances with their possible structures.SCN 4-15a

Atomic structure and bonding related to properties of materials. National 4

Atomic structure and bonding related to properties of materials. National 5

Learning Outcomes – Structure, Bonding & Properties of 32

Name


Circle a face to show how much understanding you have of each statement: if you fully understand enough to do what the outcome says, if you have some understanding of the statement, and if you do not yet understand enough to do what the statement says. Once you have completed this, you will be able to tell which parts of the topic that you need to revise, by either looking at your notes again or by asking for an explanation from your teacher or classmates.

National 4 Learning Outcomes

By the end of this topic I will be able to:

1. State that every element is made up of very tiny particles called atoms.

2. Describe the atom as having a very small positively charged nucleus with negatively charged electrons moving around outside the nucleus.

3. Describe the location and charge of the proton, neutron and electron.

4. State the relative masses of the proton, neutron and electron.

5. State that an atom is neutral because the positive charge of the nucleus is equal to the sum of the negative charges of the electrons.

6. State that an atom is neutral because the numbers of protons and electrons are equal.

7. State that atoms of different elements are different and have a different number on the Periodic Table called the atomic number.

8. State that the electrons in an atom are arranged in energy levels.

9. State the electron arrangements of the first of 32

Lesmahagow High School Structure Bonding & Properties20 elements.

10. Explain the structure of the Periodic Table in terms of the atomic number and chemical properties of the elements.

11. State that elements with the same number of outer electrons have similar chemical properties.

12. State that an atom has a mass number which equals the number of protons plus neutrons.

13. Calculate the number of neutrons, protons and electrons from the mass number and atomic number, and vice versa.

14. State that atoms can be held together by bonds.

15. State that atoms can lose, gain or share electrons to achieve a stable electron arrangement.

16. Describe the covalent bond in terms of non-metal atoms sharing pairs of outer electrons.

17. State that a molecule is a group of (usually) non-metal atoms held together by covalent bonds.

18. State that a diatomic molecule is made up of two atoms.

19. Give examples of elements which exist as diatomic molecules.

20. State that covalent compounds can exist as molecules and also as giant covalent network structures.

21. State that an ion is an atom which has either lost or gained electrons to become a charged particle.

22. Describe that an ionic compound forms when of 32

Lesmahagow High School Structure Bonding & Propertiesmetal atoms join to non-metal atoms by transferring electron(s) from the metal to the non-metal, forming a giant lattice of oppositely charged ions held together by ionic bonds.

23. Describe the ionic bond in terms of an attraction between oppositely charged ions (e.g. between a positive metal ion and a negative non-metal ion).

24. State that the chemical formula gives the number of atoms of each element in a molecule of a covalent substance.

25. State that the chemical formula gives the ratio of atoms of each element in a giant covalent network substance.

26. State that the chemical formula gives the ratio of ions of each element in an ionic substance.

27. State that metal elements and carbon (graphite) are conductors of electricity and that most non-metal elements are

non-conductors of electricity.

28. State that covalent compounds (in any state) do not conduct electricity.

29. State that ionic compounds (made from metal ions and non-metal ions) do not conduct electricity in the solid state but do conduct when dissolved in water or when molten.

30. State that electric current is a flow of charged particles.

31. State that electrons flow through metals and ions flow through solutions and ionic melts.

32. State that electrical energy chemically changes of 32

Lesmahagow High School Structure Bonding & Propertiesa molten ionic compound or a solution which conducts by breaking ionic bonds.

33. Explain why an ionic melt /solution conducts but the solid does not.

34. State that solid compounds can be ionic lattices or covalent networks and that compounds which exist as liquids or gases at room temperature are covalent molecules.

National 5 Outcomes

35. I can explain what an isotope is and state that most elements exist as a mixture of isotopes

36. I can state what is meant by relative atomic mass and explain why the relative atomic mass of an element is rarely a whole number

37. I can state that there are two different types of bonding (ionic (ionic and covalent) when elements join together, which affect the properties of their compounds

38. I can state that atoms of non-metal elements form covalent molecules

39. I can state that covalent compounds (solid, liquid, in solution) do not conduct electricity

40. I can state that ionic compounds do not conduct electricity when solid, but they do conduct when dissolved in water and when molten

41. I can show covalent bonding as a sharing of electrons

42. I can state the covalent bond is a result of two

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Lesmahagow High School Structure Bonding & Propertiespositive nuclei being held together by their common attraction for the shared pair of electrons and covalent) when elements join together, which affect the properties of their compounds

43. I can show covalent bonding as a sharing of electrons by drawing non-metal atoms joined in a molecule

44. I can use diagrams to show the shape of simple two-element molecules.

45. I can state that atoms of non-metal elements form covalent compounds.

46. I can state that a covalent network structure consists of a giant lattice of covalently bonded atoms.

47. I can describe the bonds between covalent molecules as weaker than the covalent bonds within molecules.

48. I can state that ionic solids exist as networks/lattices of oppositely charged ions (charged particles).

49. I can state what is meant by ‘valency’ of an element.

50. I can write the chemical formulae of two element compounds.

51. I can explain what the endings –ide, -ate and –ite mean.

52. I can state that a diatomic molecule is made up of two atoms and I can name the seven diatomic elements.

53. I can write formulae for compounds using prefixes, including mono-, di-, tri-, tetra-.

54. I can work out chemical formulae using valencies.

55. I can state that metal elements (solids, liquids) and carbon (graphite) are conductors of electricity because they contain mobile/delocalised electrons.

56. I can state metallic bonding is the electrostatic of 32

Lesmahagow High School Structure Bonding & Propertiesforce of attraction between positively charged ionsand delocalised electrons.

57. I can explain why ionic compounds do not conduct electricity when solid, but they do conduct when dissolved in water and when molten.

58. I can state that when ionic compounds dissolve in water, the lattice breaks up completely.

59. I can write formulae for compounds involving complex ions, eg Na2SO4.

60. I can write a word equation for a chemical reaction.

61. I can write simple symbol equations from word equations.

62. I can identify and use state symbols appropriately.

63. I can write formulae equations and balance them to show the relative number of moles of reactant(s) and product(s).

64. I can calculate the gram formula mass of a substance from the relative atomic masses of the elements within it .

65. I can state that the gram formula mass of any substance is known as one mole.

66. I can calculate the number of moles from the mass of a substance and vice versa.

67. I can calculate the mass of a reactant or product using a balanced equation.

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Lesmahagow High School Structure Bonding & PropertiesRates of Reactions – Summary notes

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National 4 Summary Notes

Atoms & Atomic Number

In order to understand the properties of elements and compounds we must look in detail at their atoms.

Everything that exists is made up of atoms. An element is a substance that is made up of atoms of only one kind. It is difficult to imagine anything as small as an atom. 100 million of them side by side will only measure about 1 cm3. A single atom is so small that it cannot be weighed on a balance. There has to be a special scale to measure the mass of something so light. The mass of an atom is measured on the relative atomic mass scale. Since this is a relative scale, it has no units. The relative atomic mass for some elements are found in the Data Booklet.

There are over 100 different elements. All the atoms of one element are different from atoms of other elements. Each different atom has a 'number'. This is called the atomic number. All atoms of the one element have the same atomic number and atoms of different elements cannot have the same atomic number. Elements are arranged in the Periodic Table in order of increasing atomic number.

Structure of the Atom

Atoms themselves consist of even smaller particles (sub-atomic particles) called protons, neutrons and electrons. The numbers of these particles vary from element to element. Protons and neutrons are found in a 'core' at the centre of the atom. This is called the nucleus. The nucleus is very small and heavy compared to the size of the rest of the atom; which is made up of mostly empty space.

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Protons have a positive charge and neutrons do not have a charge, i.e. they are neutral. Therefore the nucleus has a positive charge (due to the protons within it). Electrons move outside of the nucleus. They have a negative charge, equal and opposite to that of protons. Atoms are neutral overall, i.e. they are neither positive nor negative. This is because the total positive charge of the protons in the nucleus is equal to the total negative charge of the electrons, i.e. the positive and negative charges balance each other.

The masses of the sub-atomic particles are measured on the atomic mass scale. On this scale, protons and neutrons have a mass of one atomic mass unit (amu). Compared to protons and neutrons, even on this scale, electrons have a very small ( almost zero) mass.

Atomic Number & Mass Number

The atomic number and the mass number provide all the information necessary to calculate the number of protons, neutrons and electrons in an atom.

The atomic number tells us the number of protons in an atom of an element. Since atoms are neutral and the charge on an electron is equal and opposite to the charge on a proton, the atomic number also gives the number of electrons in an atom.

The mass number of an atom is the number of protons (atomic number) plus the number of neutrons in the atom. Note that the mass number of an atom cannot be found in the Data Booklet, you will be given it. If you want to calculate the number of neutrons in an atom it is the mass number minus the atomic number.

Some people get mixed up which number is which for an atom. Just remember the mass number is always bigger than the atomic number (think massive).

Electron arrangement

Most of the atom is empty space and electrons move through this space. The electrons do not however move in a haphazard

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fashion; they are arranged in a particular way. Electrons are arranged in shells. There is a limit to the number of electrons each shell can hold.

The first shell (nearest the nucleus) can hold 2 electrons. The second shell can hold 8 electrons. The third shell can hold 8 electrons (for the first twenty elements).

Electrons always fill the shells nearest the nucleus first. The electron arrangement of atoms of all elements is given in the Data Booklet.

From second year we know that group 1 is called the alkali metals, group 2 is the alkaline earth metals, group 7 is the halogens and group 8/0 is the noble gases.

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All the atoms of elements in the one group have the same number of electrons in the outer shell and this number is equal to the group number, e.g. 1 outer electron for all the atoms of the group 1 alkali metals and 7 outer electrons for all the atoms of the group 7 halogens. The chemical reactions of an element depend on the number of electrons in the outer shell. This is why all elements in a group have similar chemical properties, e.g. all the alkali metals are very reactive.

The noble gas family of group 8 all have a full outer electron shell. Helium only has two electrons so it has a full 1st (and only) electron shell, all the others have 8 outer electrons just like their group number, meaning a full outer electron shell. It is this full outer electron shell which gives the noble gases their stability and means they do not react with other elements to form compounds.

Bonding

Not all elements in the periodic table join with other elements to form compounds. The noble gases have a full outer electron shell (which is very stable) meaning they do not form compounds. The other elements in the periodic table have an unstable electron arrangement which means that they do form bonds to other elements forming compounds, since this helps them to achieve a stable electron arrangement like a noble gas. To achieve a stable electron arrangement atoms can lose, gain or share electrons.

When particles in elements or compounds join this ‘join’ is called a bond. There are two main kinds of bonds which we of 32

helium 2

krypton 2, 8, 18, 8xenon 2, 8, 18, 18, 8


will learn about; covalent and ionic. The type of bonding depends on the types of elements which are joined together. Covalent bonding is normally when non-metal atoms join together and ionic bonding is when a metal and a non-metal are joined.

Covalent Bonding

Covalent bonds form when atoms of non-metal elements join with other atoms of non-metal elements by sharing outer electrons. The shared electrons lie in an overlap region so that they are close enough to each element giving each element a full outer electron shell (and stability) like a noble gas. Covalent bonds can form between two atoms of the same element (forming an element) or can form between atoms of different elements (forming a compound).

It is possible for more than one covalent bond to form between atoms. We commonly represent a single covalent bond (one shared pair of electrons) in a simple diagram as a single line. Double covalent bonds (two shared pairs of electrons) are represented by a double line and triple covalent bonds (three shared pairs of electrons) are represented by a triple covalent bond.

A group of non-metal atoms held together by covalent bonds is called a molecule. Molecules made up of only

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two atoms are called diatomic molecules, e.g. hydrogen chloride. HCl (one carbon atom and one chlorine atom), and carbon monoxide, CO, (one carbon atom and one oxygen atom).

Certain elements normally exist as diatomic molecules. Since diatomic molecules contain two atoms, the chemical formula for an element that is made up of diatomic molecules is X2 (where X is the symbol for the element), e.g. hydrogen is written H2. The seven common elements that exist as molecules made up of two-atom units are hydrogen (H2), oxygen (02), nitrogen (N2), fluorine (F2), chlorine (Cl2), bromine (Br2) and iodine (I2).

In five elements including hydrogen the two atoms in the molecule share electrons to form a single covalent bond. In oxygen, the two atoms in the molecule share electrons to form a double covalent bond. In nitrogen, the two atoms in the molecule share electrons to form a triple covalent bond.

The memory aid HON7 can be used to remember the 7 diatomic elements (i.e. Hydrogen, Oxygen, Nitrogen and the top 4 elements in group 7). Or I Bring Clay For Our New House.

Ionic Bonding

In covalent bonding atoms shared outer electrons to achieve a stable electron arrangement like a noble gas.

In ionic bonding electrons are lost (transferred) from metal atoms and gained by non-metal atoms to form charged particles called ions. Since electrons have a negative charge, metal atoms will be left with a positive charge and non-metal atoms will have gained a negative charge. of 32


These oppositely charged ions are attracted to one another and when they join this is called an ionic bond.

The transfer of one electron from the lithium atom to the chlorine atom gives the lithium ion the stable electron arrangement of helium (2) and the chloride ion the stable electron arrangement of argon (2, 8 ,8). The formula for lithium chloride is LiCl.

Note that when lithium chloride actually forms it is not just one single lithium ion which bonds on to one single chloride ion but a huge number of each ion bonding together to form a huge structure called an ionic lattice. We will learn more about the nature and properties of ionic lattices in future.

Chemical Formulae

The chemical formula represents different things depending on the type of bonding present in the substance.

When the substance is a covalent molecule (with a fixed and usually small number of atoms) the formula gives the number of actual atoms of each element in the molecule.

When the substance is a giant ionic compound (with no fixed number of ions) the formula gives the ratio of the different ions of each element in the substance.

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There is another type of covalent substance which exists, called covalent network. This type of substance is a giant structure with no fixed number of non-metal atoms all bonded together by covalent bonds. The formula for this type of compound gives the ratio of atoms of each element in the substance. We will look at the covalent network in more detail during NAT 5 chemistry.

Chemical Formulae From Diagrams/Models

The easiest way to work out a chemical formula is by counting the number of each kind of atom. This method of working out formulae is only for covalent molecules as these are the only substances with a fixed number of atoms. Note that each symbol is written with the number of atoms of that element written as a subscript immediately after the symbol. When formulae are written from diagrams or models the order in which the different symbols are placed is not important.

2 hydrogens 3 carbons and and 1 oxygen 8 hydrogens Formula H2O Formula C3H8

Most chemical formulae have to be worked out from the name of the compound.

Chemical Formulae From Names Including A PrefixSometimes the name of a compound contains a prefix which allows us to write the formula. Prefixes such as mono (one), di (two), tri (three), tetra (four), penta (five), hexa (six) when present before the name of an element tell you how many atoms of that element are in the compound.

E.g. carbon dioxide contains one carbon and two oxygens (CO2). of 32

HH

O


and diphosphorus pentachloride contains two phosphorus atoms and five chlorine atoms.

Valency Method For Writing Formulae

If and only if the name of the compound does not contain a prefix the chemical formula should be worked out by using the valency method. Valency is the combining power of an element i.e how many bonds that element can form.

The valency of an element can be found from the group number in the Periodic Table.

Group Group 1 Group 2 Group 3 Group 4 Group 5 Group 6 Group 7Valency 1 2 3 4 3 2 1

Note that the group 8 noble gases do not have a valency because they are unreactive and do not form compounds.

Transition metals can form ionic compounds when joined with non-metals. The metals in this block are a bit unusual as they have no group number to give you the valency the valancy can change.

For transition metals the valency of the metal ion is given in roman numerals inside brackets immediately after the name or symbol of the metal. If no roman numeral is given, the valency is assumed to be 2.

e.g. In iron(II) oxide the valency (combining power) of the iron ion is 2 but in iron (III) oxide the valency of the iron ion is 3.

The steps for the valency method are summarised by remembering SVSDF.

Step 1 – Write the Symbol for each element.Step 2 – Write the Valency for each element.Step 3 - Swap the valencies over. of 32


Step 4 – Divide both numbers to get the smallest possible whole numbers.Step 5 - Write the Formula (including the symbol and

numbers as subscripts).

e.g. silicon oxide e.g. Iron (III)oxide

S Si O S Fe OV 4 2 V 3 2S 2 4 S 2 3D 1 2 D 2 3F SiO2 F Fe2O3

Note that the subscript 1 when it appears for an element (like for silicon above) is not written. Note also that sometimes it is not possible to divide the numbers any further in step 4 (like for iron oxide above).

Remember; never use valency method when a compound name contains prefixes.

Properties of Substances

The different types of compounds have different properties including state at room temperature and the ability to conduct electricity.

State at Room Temperature

Most elements are solid at room temperature. There are two liquid elements, bromine and mercury.

The state of a compound at room temperature is an indication of the type of bonding in the compound. If a compound is solid at room temperature that compound could be a giant ionic lattice or a giant covalent network. Any compounds which exist as liquids or gases at room temperature must be covalent molecules.

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Conductivity

Electricity is a flow of charged particles. What happens when a substance is included as part of an electrical circuit gives information about the particles in the substance and the way they are held together.

The terminals through which the electrical current enters and leaves the substance under test are called the electrodes. These are usually made of graphite, a form of carbon that conducts electricity but is comparatively unreactive. Elements and compounds that conduct electricity are conductors. Elements and compounds that do not conduct electricity are non-oonductors or insulators.

Elements: Conductors Or Non-Conductors?

The elements in the Periodic Table can be divided into metals and non-metals. Atoms are made up of a nucleus that contains positive particles. Negatively charged particles called electrons move around outside the nucleus. In metals, the outer electrons are loosely held and can move from atom to atom. The flow of electricity in metals is a flow of the loosely held electrons in a definite direction. This only happens with metal elements and is therefore why most non-metals do not conduct electricity.

The one exception to this rule is carbon in the form of graphite. This is because there are also some free moving (delocalised) electrons between the layers in the structure of graphite.

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Covalent Compounds: Conductors Or Non- Conductors?

Covalent compounds are (usually) made up of atoms of only non-metal elements held together by covalent bonds. For a substance to conduct electricity it must have charged particles which can flow. Covalent substances do not have mobile charged particles therefore do not conduct electricity.

Ionic Compounds: Conductors Or Non-Conductors?

Compounds that contain both a metal and a non-metal element are called ionic compounds. Ionic compounds are made up of charged particles called ions. In the solid, the forces of attraction keep the ions locked together. Since ions in a solid are unable to move, the solids do not conduct electricity (since no flow of charged particles). When an ionic substance is dissolved in water to form a solution or when an ionic solid is heated until it melts, the lattice is broken up. Ions therefore become free to move and so the substance is able to conduct (it now has charged particles which can flow).

Properties of Compounds summary

Covalent IonicNon-conductors Conductors if molten or in

solutionSmall forces between molecules Strong forces between ions

Low melting/boiling points High melting/boiling pointsLess dense than ionic

compoundsDenser than covalent

compoundsSoluble in covalent liquids Soluble in polar liquids (e.g.

water)Liquid over a narrow temp. range Liquids over a wide temp. range

Often liquids or gases at room temp

Always solid at room temperature

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Writing Equations Using Symbols & Formulae

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An equation using symbols and formulae gives more information than a word equation. It shows the nature of the substances involved when they are reactants and products. These equations are usually combined with state symbols after the formulae of substances.

The following state symbols are used;(s) solid (l) liquid (g) gas (aq) dissolved in water i.e. aqueous

Example Zinc metal reacts with copper (II) chloride solution to produce zinc (II) chloride solution and copper metal.

The word equation for this reaction: Zinc + copper (II) chloride zinc (II) chloride + copper

This equation can be written using symbols and formulae as: Zn (s) + CuCl2 (aq) ZnCl2 (aq) + Cu (s)

Note that zinc and copper are both elements which are not diatomic so we just use their symbol from the periodic table. Copper (II) chloride and zinc (II) chloride are both compounds with no prefix in their names so we must use SVSDF to work out their formulae.

The flow diagram on the next page can be used when writing equations involving symbols and formulae. It should be followed for each substance in the equation in turn.

National 5 Summary notes

Isotopes & Relative Atomic Mass A sample of chlorine gas actually contains two different types of atom – both types of atom have the same atomic

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number (so same number of protons) but a different mass number (or number of neutrons)These different types of atoms – with the same atomic number but a different mass number – are called isotopes.

Calculation of Relative Atomic Mass

An individual atom has a mass number. Relative atomic mass is the average mass of all isotopes present, taking into account their relative proportions.

E.g. 75% of chlorine have the mass number 35 and 25% of chlorine have a mass of 37.

Relative Atomic Mass = total mass of all atoms in the sample

Number of atoms in the sample

= (75 X 35) + (25 X 37) = 35.5100

Shapes of molecules

Bonds that are formed give molecules a distinctive shape. The shapes are caused by the repulsion of electrons that are in the bonds. Particles with the same charge move away from each other. The electrons in a covalent bond repel the electrons in other covalent bonds causing them to move as far away from each other as possible.

Tetrahedral molecules – Methane (CH4) is an example of a tetrahedral molecule. Other molecules with a similar formula have the same shape e.g. CCl4 (carbon tetrachloride)

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Pyramidal molecules – Ammonia (NH3) is an example of a pyramidal molecule.

Linear molecules – Hydrogen fluoride (HF) is an example of a linear molecule.

Bent molecule – water (H2O) is an example of a bent shaped molecule

Complex Ions

A complex ion contains more than one kind of atom e.g. carbonate, CO3

2-. These can be found in the data booklet on bottom of page 4.

Name of ion Overall charge

Formula

Ammonium +1 NH4+Hydroxide -1 OH-

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Permanganate -2 MnO42-

Dichromate -2 Cr2O72-

Formulae for Ionic Compounds with Complex ions

You must use valency rules to work out the formula of compounds that end in –ite or –ate. It is useful to write the formula for the ion in brackets e.g.Ammonium SulphateS (NH4

+) (SO42-)

V 1 2S 2 1D (Divide not needed here)F (NH4

+)2(SO42-)

Word equationsA word equation is a statement showing the reactants on the left separated by an arrow from the products on the right. For example, zinc combines with oxygen to form zinc oxide. The word equation for this is:

zinc + oxygen zinc oxide

Word Equations to Chemical EquationsWhen we know what the reactants and products are we can change the word equation into a chemical equation. You swap the words for chemical formula. of 32


e.g. for the word equation:zinc + oxygen zinc oxide

1. Look for the symbol for zinc in the data booklet page 4 (Zn). Zinc is NOT one of the diatomic elements so appears on it’s own.

2. Look for the symbol for oxygen (O). Oxygen is one of the diatomic elements for the chemical formula is O2.

3. The chemical formula for zinc oxide can be worked out using the valency method on page 19.

The chemical equation would be:Zn + O2 ZnO

Balancing Chemical Equations

Remember that the number of atoms present at the start of the reaction are the same atoms present at the end. We should be able to see this in a chemical equation.Example

N2 + H2 NH3

This equation is not balanced. There are 2 nitrogen atoms on the left hand side, but only 1 on the right. Also, there are only 2 hydrogen atoms on the left, but 3 on the right. The answer to this is that substances do not always react in a 1:1 ratio, producing 1 product molecule. In this case, 2 molecules of ammonia are formed, which accounts for the 2 nitrogens originally present.

N2 + H2 2 NH3

The 6 hydrogens needed to form the ammonia must come from not 1, but 3 hydrogen molecules.

N2 + 3 H2 2 NH3

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The equation is now balanced.

Formula Mass

The formula mass of a substance is the sum of the relative atomic masses of all the atoms shown in the formula.e.g. Sodium Nitrate has the formula NaNO3

This represents one sodium atom, one nitrogen atom and three oxygen atoms.Use page 4 of data booklet to add masses of the atoms together1 x Na = 1 x 23 = 231 x N = 1 x 14 = 143 x O = 3 x 16 = 48Formula Mass = (23 + 14 + 48) = 85g

For complex ions it is often easier to keep brackets round ions to help work out formula mass. Remember that all atoms shown inside a bracket must be multiplied by number outside bracket e.g. (NH4

+)2(SO42-)

So . (NH4+)2 shows 2 nitrogen atoms and 8 hydrogen atoms

(SO42-) shows 1 sulphur and 4 oxygen atoms

Use page 4 of data booklet to add masses of the atoms together2 x N = 2 x 14 = 281 x S = 1 x 32 = 324 x O = 4 x 16 = 648 x H = 8 x 1 = 8Formula Mass = (28 + 32 + 64 + 8) = 132g

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The MoleOne mole of a substance (n) is the formula mass expressed in grams.To find the mass of 1 mole, work out the formula mass in grams e.g.1 mole of HCl = 1 xH + 1 x Cl = 1 +35.5 = 36.5g0.2mole of NaCl = 0.2 x(1 xNa + 1 x Cl) = 0.2 x (23 + 35.5) = 11.7g

In the second example the number of moles (n) x mass of 1 mole (m) gives us the answer.

Using the triangle below we can convert moles into mass and vice versa:

Cover what you are asked to find and use the letters left e.g. how many moles are present in 18g of water?n = m / FM = 18 / 18 = 1 mole

Mole and Mass Calculations in balanced equations

By using the formula masses in grams (moles) we can deduce what masses of reactants to use and what mass of products will be formed Example 1

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m

n FM

M = mass of a substancen = number of molesFM = Formula Mass


What mass of oxygen will react with 1 mole of carbon and how much carbon dioxide is formed ?

carbon + oxygen carbon dioxide

Balanced Equation C + O2

CO2

No moles in equation 1 mole 1 mole 1 moleFormula mass 12 + 2 x 16

12+(2x16)Mass in calculation 12g 32g 44g

So we need 32g of oxygen to react with 12g of carbon and 44g of carbon dioxide is formed in the reaction.

Example 2What mass of carbon dioxide will I get when 5 grams of calcium carbonate reacts with excess HCl ? Balanced Eq: CaCO3 + 2HCl CaCl2 + CO2 + H20No moles eq: 1 mole 1 moleFormula mass 40+12+(3x16)

12+(2x16) 100g 44g

So 5 g 5/100 x 44 = 2.2g

Structure, Bonding & Properties of 32


National 4 GlossaryWord Meaning(aq) Dissolved in water.(g) Gaseous state(l) Liquid state(s) Solid state.Ammeter A device used to measure the quantity of

electricity flowing in a circuit.Atom The smallest particle of an element that can exist

on its own.Atomic mass unit The mass of one proton or one neutron (shorthand

amu).

Atomic number The number of protons in the nucleus of an atom.Bond Force of attraction between particles which holds

them together.Circuit A pathway for electricity.Conductor Substance which allows the passage of electricity

through it.Covalent Two or more non metal atoms joining together by

sharing outer electrons. Covalent network A massive structure made of lots of non-metal

atoms held together by strong covalent bonds.Delocalised electrons

Electrons which are free to move as they do not belong to any one atom.

Diatomic Two atoms joined together in a molecule.Electricity A flow of charged particles. Either electrons in

wires or ions in a solution or ionic melt.

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Word Meaning

Electrode A solid rod which conducts electricity. Can be made of graphite or a metal.

Electron Sub atomic particle with a negative charge and negligible mass. Found outside the nucleus in electron shells.

Electron arrangement

The way electrons fill electron shells.

Electron shells Area where electrons are orbiting.Formula The symbols and numbers that represent the ratio

of different atoms/ions in a substance. Graphite A covalent network made of carbon atoms. It has

delocalised (free moving) electrons which allow it to conduct electricity.

Insulator A substance which does not allow the passage of electricity through it.

Ionic compound When a metal and non metal join together by transfer of electrons. Oppositely charged ions are formed which bond (attract) together.

Ionic lattice A massive three dimensional structure where the ions are held firmly in place by strong ionic bonds.

Ions Atoms which have lost or gained electron(s) to become either positively or negatively charged.

Mass number The sum of protons and neutrons in the nucleus of an atom.

Metallic bonding Type of bonding which exists in metal elements.

Molecule A small group of non-metal atoms that are chemically joined together by covalent bonds. Has a definite number of atoms.

Neutral Not charged.

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Word MeaningNeutron Particle with no charge and mass of 1 amu. It is

located in the nucleus. Nucleus Centre of an atom containing protons and

neutrons.Outer electrons Electrons located in the outer electron shell

(furthest from the nucleus)Power pack (lab pack)

A source of electricity for use in experiments.

Prefix A few letters placed before a word e.g. mono, di, tri, tetra, penta, hexa.

Proportion / Ratio The quantity of one substance compared to another.

Proton Positively charged subatomic particle with mass of 1 amu. It is located in the nucleus.

Stable Has a full outer shell of electrons.Valency The combining power of an element (i.e. the

number of bonds an atom/ion forms in order to achieve a full outer shell of electrons like a noble gas).

Word MeaningBalanced Equation

Same number of atoms on the left hand side of an equation as on the right hand side.

Complex ion Ion which contains more than one type of atomFormula mass The sum of the relative atomic masses of all the

atoms shown in the formula.Mole One mole of a substance (n) is the formula mass

expressed in grams.

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National 5 Glossary

elements, mixtures and compounds … · web viewthe seven common elements that exist as molecules...

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