ch. 22 chemical bonds. what is a chemical formula? when elements combine to form compounds a...

Ch. 22 Chemical Bonds

What is a Chemical Formula?• When elements combine to form compounds a

chemical reaction occurs creating a new compound with properties that are different from the original elements.

• When a new compound is formed it has a new chemical formula. A chemical formula tells what elements a compound contains and the exact number of atoms of each element in a unit of that compound.

• Example: 2Na + Cl2 2NaCl

Why do atoms form compounds?

• The electric forces between electrons and protons (which are oppositely charged) hold atoms and molecules together which cause compounds to form.

• But, not all atoms form compounds readily. Noble gases already have all the electrons they need! In other words, their outer energy level is completely filled.

• When an atoms outer energy level is filled, they are considered chemically stable.

How do atoms become chemically stable?

• When an atom is not chemically stable, it must bond with another atom to become stable. To do this, an atom must gain or lose electrons becoming an ion. An ion is a charged particle because it now has either more or fewer electrons than protons.

• A cation is an atom that has given away an electron in its outer energy level (valence electron) and is now a positively charged.

Howdo atoms become chemically stable?

• An anion is an atom that has gained an electron in its outer energy level and is now a negatively charged particle.

Types of Chemical Bonds

• A chemical bond is the force that holds atoms together in a compound.

• There are 2 main types of chemical bonds: Ionic and Covalent bonds

Ionic Bonds

• An ionic bond is the bond that occurs when a metal gives away a valence electron (becomes a cation) and a nonmetal gains the valence electron (becomes an anion). In other words, it’s a bond between a metal and a nonmetal!

• Form crystalline solids• High melting and boiling points• Conduct electricity when melted• Many are soluble in water• Strong attraction between positive and negative ions• Brittle and hard

Bozeman video

• http://www.bozemanscience.com/chemical-bonds-covalent-vs-ionic

Ionic Bonds

• There are 2 ways to show ionic bonding:• Electron – dot method:

• The criss cross method:

Make sure to reduce when necessary!

Ionic Bonds

• Sometimes compounds only involve 2 elements. These are called Binary compounds.

• To name binary ionic compounds:1. Write the name of the metal first (capitalized).2. Write the name of the nonmetal (lower case).3. Change the ending of the nonmetal to –ide.• Example: NaCl Sodium chloride• MgCl2 Magnesium chloride

Ionic Bonds

• Oxidation number is the charge on the ion. This is what we use for the criss cross method. For metals, it is the number of valence electrons available for bonding. For nonmetals, it is the number of valence electrons needed to fill the outer energy level.

• Example: Na+1 and Cl-1 • Mg+2 and I-1

Ionic Bonds• Some compounds involve more than 2 elements. These

compounds contain polyatomic ions. Polyatomic ions are a covalently bonded group of atoms that ionically bond with an ion of opposite charge.

• To name compounds with polyatomic ions:1. Write the name of the positively charged ion first. If it is a

single metal, write it’s name capitalized. If it is a polyatomic ion, use it’s name also capitalized.

2. Write the name of the negatively charged ion second. If it is a single non-metal, remember to change the ending to –ide. If it is a polyatomic ion, use it’s name and DO NOT change the ending.

• Example: NaSO4 Sodium sulfate

• NH4Cl Ammonium chloride

Covalent Bonds

• Covalent bonds form between nonmetals. It is the attraction they form when sharing electrons.

• Once a covalent bond is formed, the resulting compound is referred to as a molecule.

• Single, Double or Triple bonds can form between 2 nonmetals.

Covalent Bonds

• Electrons are not always shared equally between the atoms in a covalent bond.

• Polar molecule is a molecule that has a slightly positive end and a slightly negative end.

• Nonpolar molecule is a molecule in which electrons are shared equally.

•

Covalent Bonds

• Properties of Covalent bonds include:• Poor conductors of heat and electricity• Lower melting and boiling points• Solid, liquids or gases• Strong bonds between atoms but weak

attraction between molecules• Soft• Do not dissolve in water

Covalent bonds

• To draw covalent bonds:• Place the element that is LEAST represented

in the middle and radiate all other elements around the central atom.

• Only place valence electrons that will be shared between the 2 atoms. Any electrons not being shared must go on the “outside” of the atom.

• Connect shared electrons with dashes.• Covelant bonds DO NOT REDUCE!

Covalent Bonds

Covalent compounds use prefixes to indicate the number of atoms per element is in the compound.

Covalent Bonds

1. The first element NEVER uses the prefix mono but does use all other prefixes. Make sure to capitalize it!

2. Write the appropriate prefix for the second element.3. Write the root of the 2nd element’s name. If the

prefix ends is o/a and the element name also begins with o/a, drop one of the o/a. Ex) mono & oxygen becomes monoxide

4. Change the ending of the 2nd element to –ide.Example) CO Carbon monoxide CO2 Carbon dioxide

P2O5 Diphosphorus pentoxide

Bozeman videos

• http://www.bozemanscience.com/naming-compounds-part-1

• http://www.bozemanscience.com/naming-compounds-part-2

Diatomic Molecules

• There are 7 nonmetals that are highly unstable. Because of this, they bond readily with another like atom. These are referred to as Diatomic Molecules because they are found naturally in pairs.

• Atoms include: H, N, O, F, Cl, Br, and I. If you look closely (with the exception of H), they make a “7” on the periodic table!

What is a hydrate?

• A hydrate is a compound that has water chemically attached to its ions and written into its chemical formula.

• To name, name the ionic compound to which it is attached. Then use the prefix for the number of hydrates and then simply end with the word “hydrate”.

• Example: CoCl2*6H2O Cobalt chloride hexahydrate

Check!!

• MgO2 Ionic or covalent bond?

• CCl4 Ionic or covalent bond?

• Name this compound: CaCl2

• Name this compound: CCl4

• Name this compound: CaSO4 * 2H2O• Polar, Nonpolar, ionic?• A) B)

• C)