objectives describe the particles within atoms and the structure of atoms. what are elements? relate...
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Objectives• Describe the particles within atoms and the structure
of atoms.
What are elements?
• Relate the energy levels of atoms to the chemical properties of elements.
• Define the concept of isotopes.
– element
– atom
– nucleus
– proton
– neutron
– atomic number
– mass number
– electron
Vocabulary – energy level
– valence electron
– isotope
– atomic mass
– radioactivity
• Matter is anything that has volume and mass.
• On Earth, matter usually can be found as a solid, liquid, or gas.
What are elements?• The physical world that surrounds you and all
living things are composed of matter.
What are elements?
Elements• All matter is made of substances called
elements.
What are elements?
An element is a substance that cannot be broken down into simpler substances by physical or chemical means.
• Ninety-two elements occur naturally on Earth and in the stars.
• Other elements have been produced in laboratory experiments.
Elements• Each element is identified by a one-, two-,
or three-letter abbreviation known as a chemical symbol.
What are elements?
Elements are Made of Atoms• Each element has distinct characteristics.
What are elements?
An atom is the smallest particle of an element that has all of the characteristics of that element.
• All atoms consist of even smaller particles: protons, neutrons, and electrons.
Elements are Made of Atoms
The nucleus, which is made up of protons and neutrons, forms the center of an atom.
What are elements?
– A proton (p+) is a tiny particle that has mass and a positive electrical charge.
– A neutron (n0) is a particle with about the same mass as a proton, but it is electrically neutral; that is, it has no electrical charge.
• All atomic nuclei have a positive charge.
Elements are Made of Atoms• The number of protons and neutrons in different
atoms varies widely.
What are elements?
– The atomic number is the number of protons in an atom’s nucleus.
– The mass number is the combined number of protons and neutrons.
An electron (e–) has little mass, but it has a negative electrical charge that is exactly the same magnitude as the positive charge of a proton.
Elements are Made of Atoms• Surrounding the nucleus of an atom are smaller
particles called electrons.
What are elements?
• An atom has an equal number of protons and electrons which produces an atom that has no overall charge.
• The mass of an atom depends mostly upon the number of protons and neutrons in its nucleus.
• The size of an atom depends upon the number and arrangement of its electrons.
Elements are Made of Atoms
An energy level represents the area in an atom where an electron is most likely to be found.
What are elements?
Electrons in Energy Levels• Electrons are distributed over one or more
energy levels in a predictable pattern.
What are elements?
• Each energy level can hold only a limited number of electrons.
– The innermost energy level can hold only 2 electrons.
– The second energy level can hold up to 8 electrons.
– The third energy level can hold up to 18 electrons.
– The fourth energy level can hold up to 32 electrons.
• Electrons tend to occupy the lowest available energy level.
Electrons in Energy Levels• The number of electrons in the outermost
energy level determines the chemical behavior of the different elements.
What are elements?
Valence electrons are the outermost electrons in an atom.
• Elements with the same number of valence electrons have similar chemical properties.
Electrons in Energy Levels• Sodium (Na) atoms, with just one valence
electron, are highly reactive metals, which means that they combine easily with other elements.
What are elements?
Electrons in Energy Levels• Elements such as helium (He), neon (Ne), and
argon (Ar) are inert, which means that they do not easily combine with other elements.
What are elements?
• This is because they have full outermost energy levels.
Isotopes• The number of neutrons in the nuclei of an
element’s atoms can vary.
What are elements?
Isotopes are atoms of the same element that have different mass numbers and the same chemical properties.
The atomic mass of an element is the average of the mass numbers of the isotopes of an element.
Isotopes• The nuclei of some isotopes are unstable and
release radiation.
What are elements?
Radioactivity is the spontaneous process through which unstable nuclei emit radiation.
• During radioactive decay, a nucleus can lose protons and neutrons, change a proton to a neutron, or change a neutron to a proton.
• Because the number of protons in a nucleus identifies an element, decay changes the identity of an element.
What Elements are Most Abundant?• The two most abundant elements in the universe
are hydrogen and helium.
What are elements?
What Elements are Most Abundant?• The percentages of elements in Earth’s crust
differ from the percentages in the universe.
What are elements?
Section Assessment
1. Match the following terms with their definitions.
___ proton
___ energy level
___ neutron
___ atom
What are elements?
A. a tiny particle that has mass and a positive electrical charge
B. the smallest particle of an element that has all of the characteristics of that element
C. a tiny particle that has mass and is electrically neutral
D. an area of an atom where an electron is most likely to be found
Section Assessment
2. What arrangement of electrons would you expect to find in an iron (Fe) atom?
____ first energy level
____ second energy level
____ third energy level
____ fourth energy level
What are elements?
_______ The number of protons can differ from atom to atom in the same element.
_______ The number of protons can differ from atom to atom in the same element.
_______ Oxygen and silicon are the most abundant elements in the universe.
_______ Elements with the same number of valance electrons have similar properties.
Section Assessment
3. Identify whether the following statements are true or false.
What are elements?
Objectives• Describe the chemical bonds that unite atoms to
form compounds.
• Relate the nature of chemical bonds that hold compounds together to the physical structures of compounds.
• Distinguish among different types of mixtures and solutions.
Vocabulary
How Atoms Combine
– compound
– chemical bond
– covalent bond
– molecule
– ion
– ionic bond
– chemical reaction
– solution
– acid
– base
Compounds
A compound is a substance that is composed of atoms of two or more different elements that are chemically combined.
How Atoms Combine
• Most compounds have totally different properties from the elements of which they are composed.
• For most elements, an atom is chemically stable when its outermost energy level is full.
Chemical bonds are the forces that hold the elements together in a compound creating a state of stability.
Compounds
How Atoms Combine
Covalent Bonds
– One way in which atoms fill their outermost energy levels is by sharing electrons.
– A covalent bond is the attraction of two atoms for a shared pair of electrons that holds the atoms together.
Compounds
How Atoms Combine
Covalent Bonds
– A molecule is composed of two or more atoms held together by covalent bonds.
– Molecules have no overall electrical charge because the total number of electrons equals the total number of protons.
Compounds
How Atoms Combine
Covalent Bonds
– Molecules are represented in chemistry by chemical formulas that include the symbol for each element followed by a subscript number that stands for the number of atoms of that element in the molecule.
– If there is only one atom of an element, no subscript number follows the symbol.
– A molecular compound is a compound comprised of molecules.
Compounds
How Atoms Combine
Polar Molecules
– When atoms in a covalent bond do not share electrons equally, they form polar bonds.
– Polar bonds have a positive end and a negative end.
– The overall shape of a molecule indicates whether it is polar.
Ions
How Atoms Combine
• Sometimes, atoms gain or lose electrons from their outermost energy levels.
A charged particle called an ion is an atom that gains or loses an electron.
• In general, an atom in which the outermost energy level is less than half-full tends to lose its valence electrons.
• When an atom loses its valence electrons, it becomes positively charged and is indicated by a superscript plus sign.
Ions
How Atoms Combine
• An atom in which the outermost energy level is more than half-full tends to fill its outermost energy level by adding one or more needed electrons.
• Such an atom forms a negative ion which is indicated by a superscript negative sign.
• If the outermost energy level is exactly half-full, an atom may form either a positive or negative ion.
Ions
How Atoms Combine
Ionic Bonds
– Positive and negative ions attract each other.
– An ionic bond is the attractive force between two ions of opposite charge.
– Positive ions are always written first in chemical formulas.
Ions
How Atoms Combine
Ionic Bonds
– With an ionic compound, the net electrical charge of the compound is zero.
– Ionic compounds are compounds formed by ionic bonding.
Metallic Bonds
How Atoms Combine
• In metals, the valence electrons are shared by all the atoms, not just by adjacent atoms.
• The positive ions of the metal are held together by the negative electrons between them.
• This type of bond, known as a metallic bond, allows metals to conduct electricity easily because the electrons can move freely throughout the entire solid metal.
Chemical Reactions
How Atoms Combine
• Sometimes, compounds break down into simpler substances.
A chemical reaction is the change of one or more substances into other substances.
• Chemical reactions are described by chemical equations.
• A chemical equation must be balanced by showing an equal number of atoms for each element on each side of the equation.
Mixtures and Solutions
How Atoms Combine
• A mixture is a combination of two or more components that retain their identities.
• When a mixture’s components are easily recognizable, such as soil, it is called a heterogeneous mixture.
• In a homogeneous mixture such as coffee, the component particles cannot be distinguished, even though they still retain their original properties.
Mixtures and Solutions
How Atoms Combine
A homogeneous mixture is also called a solution.
• A solution may be liquid, gaseous, or solid.
– Seawater is a liquid solution consisting of water molecules and ions of many elements that exist on Earth.
– Air is a solution of gases, mostly nitrogen and oxygen molecules together with other atoms and molecules.
– Bronze is a solid solution of copper and tin atoms.
Mixtures and Solutions
How Atoms Combine
Acids and Bases
– An acid is a solution containing a substance that produces hydrogen ions (H+) in water.
– Many chemical reactions that occur on Earth involve solutions called acids and bases.
– The most common acid in our environment is carbonic acid, which is produced when carbon dioxide is dissolved in water by the following reaction.
H2O + CO2 H2CO3
– The most common acid in our environment is carbonic acid, which is produced when carbon dioxide is dissolved in water by the following reaction.
H2O + CO2 H2CO3
Mixtures and Solutions
How Atoms Combine
Acids and Bases
– Some of the carbonic acid molecules in the water dissociate, or break apart, into hydrogen ions and bicarbonate ions, as represented by the following equation.
H2CO3 H+ + HCO2–
– Bases produce hydroxide ions (OH–) in solution.
Mixtures and Solutions
How Atoms Combine
Acids and Bases
– A base can neutralize an acid by combining with hydrogen ions of the acid to form water through the following reaction.
H+ + OH– H2O
– The pH scale measures the hydrogen and hydroxide ions in solutions on a scale of 0 to 14, with 7 being neutral.
– The pH scale measures the hydrogen and hydroxide ions in solutions on a scale of 0 to 14, with 7 being neutral.
Mixtures and Solutions
How Atoms Combine
Acids and Bases
– A solution with a pH reading below 7 is considered to be acidic.
– A solution with a reading above 7 is considered to be basic.
Section Assessment
1. Match the following terms with their definitions.
___ covalent bond
___ compound
___ ion
___ acid
How Atoms Combine
A. an atom that gains or loses an electron and becomes electrically charged
B. a solution containing a substance that produces hydrogen ions in water
C. an attraction of two atoms for a shared pair of electrons that hold the atoms together
D. a substance that is composed of atoms of two or more different elements that are chemically combined
Section Assessment
How Atoms Combine
2. Identify whether the following are acidic, basic, or neutral.___ Milk
___ Distilled water
___ Rainwater
___ Ammonia
___ Lemon
___ Tomato
___ Antacid
A. Acidic
B. Basic
C. Neutral
Section Assessment
3. Describe the following chemical equation:
S + O2 SO2
How Atoms Combine
• crystalline structure
• glass
• evaporation
• sublimation
Objectives• Describe the states of matter on Earth.
• Explain the reasons that matter exists in these states.
• Relate the role of thermal energy to changes of state in matter.
Vocabulary
States of Matter
• plasma
• condensation
Solids• Solids are substances with densely packed
particles, which may be ions, atoms, or molecules, depending upon the substance.
States of Matter
• The particles of a solid are arranged in a definite pattern; thus, a solid has both a definite shape and a definite volume.
Most solids have a crystalline structure, in which the particles are arranged in regular geometric patterns.
Solids• Crystals form symmetrical solid objects with flat
faces and straight edges between faces.
States of Matter
• The angles between the faces depend upon the internal arrangement of the particles.
Solids• When many crystals form in the same space
at the same time, mutual interference results in a mass of intergrown crystals, called a polycrystalline solid.
States of Matter
• Most solid substances on Earth, including rocks, are polycrystalline materials.
Glasses are solids that consist of densely packed atoms arranged at random.
• Glasses do not form crystals, or their crystals are so small that they cannot be seen.
Liquids• The atoms in solids vibrate at any temperature
above absolute zero (2273°C).
States of Matter
• These thermal vibrations increase with increasing temperature.
• At the melting point of the material, the vibrations break the forces holding the solid together.
• The particles can then slide past each other, and the substance becomes liquid.
• While liquids do not have their own shape, they do have definite volume.
Gases• Individual particles in a liquid may gain sufficient
energy to escape the liquid.
States of Matter
Evaporation, or vaporization, is the process of changing from a liquid to a gas.
• When any liquid reaches its boiling point, it vaporizes quickly and becomes a gas.
Sublimation is the slow change of state from a solid to a gas without an intermediate liquid state.
Gases• In gases, the particles are separated by relatively
large distances and move about at extremely high speeds.
States of Matter
• Gas particles move independently of each other and travel randomly.
• Gases have no definite shape or volume and can expand into any space available, unless they are restrained.
• Earth’s gravity keeps the gases in the atmosphere from escaping into space.
The Electromagnetic Spectrum• Satellites detect different wavelengths of energy
reflected or emitted from Earth’s surface.
States of Matter
• This energy has both electric and magnetic properties and is referred to as electromagnetic radiation.
• Electromagnetic radiation includes visible light, gamma rays, X rays, ultraviolet waves, infrared waves, radio waves, and microwaves.
Plasma• At temperatures greater than 5000°C, the
collisions between particles are so violent that electrons are knocked away from atoms.
States of Matter
• Such extremely high temperatures exist in stars, and, as a result, the gases of stars consist entirely of positive ions and free electrons.
Plasmas are hot, highly ionized, electrically conducting gases.
Changes of State• Solids melt when they absorb thermal energy and
their temperatures rise.
States of Matter
• When a liquid absorbs thermal energy from the environment, it evaporates.
• When a liquid freezes, the same thermal energy is then released back into the environment.
• When a gas is cooled, it releases thermal energy in the process of condensation.
Condensation is the change from a gas to a liquid.
Conservation of Matter and Energy• The law of conservation of matter states that
matter cannot be created or destroyed but can change from one form to another.
States of Matter
• The law of the conservation of energy, also called the first law of thermodynamics, states that energy cannot be created or destroyed but it can be changed from one form to another.
Section Assessment
1. Match the following terms with their definitions.
___ crystalline structure
___ glasses
___ evaporation
___ sublimation
States of Matter
A. solids that consist of densely packed atoms arranged at random
B. a slow change from a solid to a vapor without an intermediate liquid state
C. a solid in which the particles are arranged in regular geometric patterns
D. the process of change from a liquid to a gas
Section Assessment
2. What are two examples of matter in the plasma state that you have seen?
States of Matter
Section Assessment
States of Matter
3. Identify whether the following processes absorb or release energy into the environment.
___ condensation
___ evaporation
___ melting
___ freezing
___ sublimation
A. Absorb energy
B. Release energy
C. Neither release or absorb
Section 3.1 Main Ideas• The basic building blocks of matter are atoms. Atoms consist
of protons, neutrons, and electrons.
• Protons have a positive electrical charge, electrons have a negative electrical charge, and neutrons are electrically neutral. Protons and neutrons make up the nucleus of an atom; electrons surround the nucleus in energy levels.
• An element is a substance consisting of atoms with a specific number of protons in their nuclei. Isotopes of an element differ by the number of neutrons in their nuclei. Many elements are mixtures of isotopes.
• The number of electrons in the outermost energy levels of atoms determines their chemical behavior. Elements with the same number of electrons in their outermost energy levels have similar chemical properties.
Section 3.1 Study Guide
Section 3.2 Main Ideas• Atoms of different elements combine to form compounds.
• Atoms held together by the sharing of electrons in covalent bonds form molecular compounds.
• Ions are electrically charged atoms or groups of atoms. Positive and negative ions attract each other and form ionic compounds.
• Acids are solutions containing hydrogen ions. Bases are solutions containing hydroxide ions. Acids and bases can neutralize each other.
• A mixture is a combination of components that retain their identities. A solution is a mixture in which the components can no longer be distinguished as separate. Solutions can be liquid, solid, gaseous, or combinations.
Section 3.2 Study Guide
Section 3.3 Main Ideas• Matter on Earth exists in three common physical states: solid,
liquid, or gaseous. Matter in the universe includes plasma.
• Most solids have a crystalline structure.
• Liquids are densely packed arrangements of particles.
• Gases consist of widely separated, individual particles. Plasmas are hot, highly ionized, electrically conducting gases.
• Changes of state involve thermal energy.
Section 3.3 Study Guide
1. Which of the following is NOT about elements?
a. They cannot be broken down into simpler substances by physical or chemical means.
b. There are 47 naturally occurring elements on Earth and in the stars.
c. All matter is made of elements.
d. Each element is identified by a chemical symbol.
Multiple Choice
Chapter Assessment
There are 92 elements that occur naturally on Earth and in the stars.
2. An element’s atomic number represents ____.
a. the number of protons in the atom’s nucleus
b. the combined number of protons and neutrons
in the atom’s nucleus
c. the number of neutrons in the atom’s nucleus
d. none of the aboveThe combined number of protons and neutrons is the element’s mass number. The number of neutrons can vary among the atoms of an element, creating isotopes.
Multiple Choice
Chapter Assessment
Multiple Choice
3. Which is the most abundant element in the universe?
a. oxygen c. iron
b. helium d. hydrogen
Chapter Assessment
Hydrogen makes up about 93.5% of all matter in the universe. It is followed by helium at 6.3%.
Multiple Choice
4. Which is the most abundant element in Earth’s crust?
a. hydrogen c. oxygen
b. silicon d. aluminum
Chapter Assessment
Oxygen makes up 46.65 of Earth’s crust. It is followed by silicon (27.7%), aluminum (8.1%), and iron (5.0%).
Multiple Choice
5. Which of the following is a molecule?
a. argon c. nitrogen
b. water d. uranium
Chapter Assessment
Argon, nitrogen, and uranium are elements.
Short Answer
6. What condition is necessary for matter to be ina plasma state?
Chapter Assessment
Short Answer
7. What three forms can a solution take?
Chapter Assessment
True or False
8. Identify whether the following statements are true or false.
______ A pH value of 11 would indicate an acid.
______ Ions are atoms that either lost or gained an electron.
______ Apple juice is an example of a solution.
______ In a polar bond, electrons are shared equally.
______ Two negative ions will join to create an ionic bond.
Chapter Assessment
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