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Chapter Introduction
Lesson 1 Atoms
Lesson 2 Elements
Lesson 3 Compounds
Lesson 4 Chemical Reactions and Energy
Chapter Wrap-Up
What happens to atoms and energy during a chemical reaction?
Essential Questions
• What is an atom and how has the model of the atoms changed over time?
Atoms
Atom
Electron
Nucleus
Proton
Atoms
Neutron
Electron cloud
An atom is the smallest particle of an element that still has the same chemical properties of the element.
What are atoms?
• Where are the electrons, neutrons, and protons located in an atom?
• What are the charges of the parts of the atom?
• How does the mass of a neutron compare to the mass of a proton?
• How does the mass of an electron compare to the mass of a proton or a neutron?
• The protons and neutrons are in the nucleus. The electrons are all located within the electron cloud.
• Electrons are negatively charged, protons are positively charged, and neutrons are neutral or no charge.
• The mass of a proton and neutron are about equal.
• The mass of an electron is 1/1,840 times smaller than a proton or a neutron.
Democritus (460–370 BC) believed that matter is made of small, solid objects called atomos, from which the English word atom is derived.
What are atoms?
What are atoms? (cont.)
• Aristotle (384–322 BC) did not believe that empty space exists, but instead believed that all matter is made of fire, water, air, and earth.
• Because Aristotle was so influential, his ideas were accepted and Democritus’s ideas about atoms were not studied again for more than 2,000 years.
• In the late 1700’s, John Dalton combined from his own scientific research with data from the research of other scientists to propose a new atomic theory.
– Dalton’s experiments indicated that matter was made of tiny particles with spaces between them.
What are atoms? (cont.)
• Not long after Dalton’s findings, another scientist, J.J. Thomson, made some important discoveries using a cathode ray tube.
What are atoms? (cont.)
• Through further experiments, Thomsom found that the rays were made of particles. He called these particles electrons.
• electron is a particle with a negative electrical charge.
What are atoms? (cont.)
• Thomson believed that atoms also contain a positive charge that balances the negatively charged electrons.
What are atoms? (cont.)
• Thomson thought an atom was a sphere with a positive charge evenly spread throughout with negatively charged electrons mixed through the positive charge.
• In the early 1900’s, scientist, Ernest Rutherford set up experiments to test Thomson’s atomic model and to learn more about what atoms contain.
• Rutherford and his students fired alpha particles at gold foil.
– Alpha particles are tiny, positively charged particles.
How was Thomson’s atomic model modified?
•Rutherford expected the positive alpha particles to travel straight through the foil without changing direction.
How was Thomson’s atomic model modified? (cont.)
• Some alpha particles traveled in a straight path, as expected. But some changed direction, and some bounced straight back.
How was Thomson’s atomic model modified? (cont.)
• Because some of the positively charged alpha particles bounced off something, the gold atoms must contain some positively charged object in the empty space.
How was Thomson’s atomic model modified? (cont.)
How was Thomson’s atomic model modified? (cont.) • Rutherford concluded that most of an
atom’s mass and positive charge is concentrated in a small area in the center of the atom called the nucleus.
• Nucleus the center of an atom, which contains most of the atom’s mass.
• Further research showed that the positive charge in the nucleus is made up of positively charged particles called protons.
– Proton a positively charged particle inside an atom’s nucleus.
• Negatively charged electrons move in the empty space surrounding the nucleus.
How was Thomson’s atomic model modified? (cont.)
• Rutherford’s model contains a small, dense, positive nucleus. Tiny, negatively charged electrons travel in empty space around the nucleus.
How was Thomson’s atomic model modified? (cont.)
• James Chadwick, Rutherford’s coworker, discovered that, in addition to protons, the nucleus also contained neutrons.
– Neutron a particle that is found in the nucleus of an atom and has no electrical charge.
How was Thomson’s atomic model modified? (cont.)
• Early in the twentieth century, Niels Bohr proposed that electrons move in circular orbits, or energy levels, around the nucleus.
How was Thomson’s atomic model modified? (cont.)
• Each energy level can hold a certain number of electrons:
– 1st energy level = 2 electrons (closest to the nucleus)
• When full, electrons begin to fill the second level.
– 2nd energy level = 8 electrons
• When full, electrons go to the next-higher level.
How was Thomson’s atomic model modified? (cont.)
• The last occupied energy level might or might not be completely filled.
• Electrons in the outermost level are called valence electrons.
– These outermost electrons are involved in chemical bonding.
How was Thomson’s atomic model modified? (cont.)
• In Bohr’s model of the atom, electrons move in circular orbits around the atom.
How was Thomson’s atomic model modified? (cont.)
• The mass of electrons is much smaller than the mass of protons or neutrons.
• Most of the mass of an atom is found in the nucleus.
What is the modern atomic model?
• In the modern atomic model, electrons form an electron cloud.
• An electron cloud is an area around an atomic nucleus where an electron is most likely to be.
What is the modern atomic model?
• The modern atomic model shows the electrons moving around the nucleus in the electron cloud. The cloud represents the area where the electrons are more likely to be found.
What is the modern atomic model?
A. atom
B. electron
C. nucleus
D. proton
Which term describes a particle with one negative charge?
Whose model of the atom contained a sphere of positive charge with negatively charged electrons within it?
A. Dalton
B. Democritus
C. Rutherford
D. Thomson
A. electron cloud
B. neutron
C. nucleus
D. proton
Which term refers to an area around an atomic nucleus where an electron is most likely to be?
Essential Question
• What are the properties of elements?
Elements
Element
Atomic number
Isotope
Elements
Average atomic mass
Periodic table
• Everything around you is made of elements.
– Elements a pure substance that cannot be broken down into a simpler substance.
What are elements?
– Ex. The human body is made mostly of water (H2O). Water is not an element because it can be broken into simpler substances of Hydrogen (H) and Oxygen (O). Hydrogen and oxygen are elements.
• Every element has a symbol that is one or two letters long.
– Ex. Hydrogen’s symbol is H
Oxygen’s symbol is O
Copper’s symbol is Cu
• The first letter is always capitalized.
• The symbols are used in chemical formulas.
What are elements? (cont.)
• Each element has atoms consisting of a specific number of protons, neutrons and electrons.
• An element is identified by the number of protons contained in each of its atoms.
– Ex. Oxygen atoms contain 8 protons
Nitrogen atoms contain 7 protons
• Atomic number the number of protons in an atom of an element.
What are elements? (cont.)
• Different elements have different atomic numbers.
• Atoms normally have the same number of electrons as protons.
What are elements? (cont.)
• Atoms of the same element can have different numbers of neutrons.
• Isotopes are atoms of the same element that have different numbers of neutrons.
• Most elements have several isotopes.
What are elements? (cont.)
• The mass number of an atom is the sum of the number of protons and neutrons in an atom.
Mass number = number of protons + number of neutrons
• An isotope is often written with the element name followed by the mass number.
What are elements? (cont.)
• Average atomic mass is the average mass of the atoms of an element.
• The average mass is weighted toward, or favors, the isotope that is most abundant.
What are elements? (cont.)
• Periodic table a chart that shows the elements in order of increasing atomic number.
– The atomic number increases from left to right as you move across a period.
• Elements on the periodic table are organized in periods (rows) and groups (columns) according to their physical and chemical properties.
What is the periodic table?
• Each box in the periodic table shows information about a different element.
– Name
– Chemical symbol
– Atomic number
– Average atomic mass
– State of matter at room temperature
What is the periodic table? (cont.)
• Scientists divide the elements into three groups based on similar properties.
What are metals and nonmetals?
• Electrical resistance is a measure of how difficult it is for an electric charge to flow through an object.
• Conductors (like metals) have low electrical resistance and allow electricity to flow easily because their atoms’ valence electrons can easily move from atom to atom.
– Ex. Electric wires are usually made of copper.
What are metals and nonmetals? (cont.)
• A good insulator has high electrical resistance.
• Atoms of an insulator hold electrons tightly and prevent electricity from moving easily through the material.
– Ex. Electrical wiring covered with plastic.
What are metals and nonmetals? (cont.)
• Elements get more metallic to the left across any row in the periodic table.
• Elements get more metallic toward the bottom of any column.
• In the middle, the properties switch from metallic to nonmetallic. These elements are called metalloids.
What are metalloids?
• Metalloids have some properties of metals and some of nonmetals.
What are metalloids? (cont.)
A. 12
B. 25
C. 24.31
D. 54.94
Use the periodic table. What is the average atomic mass of magnesium?
A. atomic number
B. average atomic mass
C. isotope
D. mass number
Which term refers to the sum of the number of protons and neutrons in an atom?
A. 44
B. 88
C. 101
D. 57
Ruthenium has an atomic number of 44 and a mass number of 101. How many protons does ruthenium have?
Essential Question
• How do atoms combine to form all types of matter?
Compounds
• Compound is a substance formed by the chemical combination of two or more elements.
– Ex. Citric acid – found in oranges and lemons – is a compound that is made of the elements carbon (C), hydrogen (H) and oxygen (O)
citric acid is written as = C6H8O7
What are compounds?
• The properties of a compound are usually different from the properties of the elements from which it is made.
– Ex. Table salt (sodium chloride)
• Sodium (Na) = soft, silvery and highly reactive metal
• Chlorine (Cl) = poisonous green gas.
• Table salt (NaCl) = white, brittle, crystalline solid
What are compounds? (cont.)
• Atoms form bonds with other atoms by losing, gaining or sharing their valence electrons.
– Ionic bonds – When a metal and a nonmetal bond, one or more valence electrons transfer from the metal atom to the nonmetal atom.
• Ion is an atom that is positively or negatively charged because it has gained or lost electrons.
How do atoms bond?
– Ionic bonds (cont.)
• Atom loses electron(s) = positively charged
• Atom gains electron(s) = negatively charged
• Two ions have opposite charge and are strongly attracted to each other.
• Ionic bond an attraction that holds oppositely charged ions close together.
How do atoms bond? (cont.)
– Covalent bonds– When nonmetal atoms bond together, they bond by sharing valence electrons.
• Covalent bond is a chemical bond that forms when atoms share electrons.
• Shared electrons move back and forth between the outer energy levels of each atom in the covalent bond.
• Form a neutral particle called a molecule.
How do atoms bond? (cont)
• Compounds that contain carbon are the building blocks of living things and are called organic compounds.
• Compounds that do not contain carbon as well as carbon monoxide and carbon dioxide are called inorganic compounds.
What compounds make up common substances?
A. neutron
B. nucleus
C. proton
D. electron
Which part of the atom is gained or lost when forming a chemical bond?
A. covalent bond
B. chemical formula
C. compound
D. polar molecule
Which term refers to chemical combinations of different types of atoms?
A. chlorine
B. calcium
C. table sugar
D. sodium
Which substance is a compound?
Essential Question
• Why do chemical reactions always involve a change in energy?
Chemical Reactions and Energy
Exothermic reaction
Endothermic reaction
Chemical Reactions and Energy
Rate of reaction
Catalyst
• Chemical bonds contain a form of energy called chemical energy.
– When a chemical bond breaks, the bond releases chemical energy.
– When a chemical bond forms, chemical energy is absorbed.
• You might feel this energy change as a change in the temperature of the surroundings.
What are exothermic reactions?
• Some chemical reactions release more energy than they absorb.
• Some chemical reactions absorb more energy than they release.
• Energy is conserved in all chemical reactions.
What are exothermic reactions? (cont.)
• Exothermic reaction is a chemical reaction that releases energy.
What are exothermic reactions? (cont.)
• In an exothermic reaction, not all the chemical energy released from breaking the reactant(s) bonds is used in the formation of the product bonds.
• Chemical reactions can release several kinds of energy: electrical, light, sound and thermal.
– Ex. Welding torch is an exothermic reaction between hydrogen and oxygen to make water that releases light energy and thermal energy.
– Ex. Energy released during digestion of food is transferred to your cells to help you grow, move and think.
• In an exothermic reaction, the energy released comes from the bonds of the reactants.
What are exothermic reactions? (cont.)
• Endothermic reaction is a chemical reaction that absorbs energy.
What are endothermic reactions? (cont)
• In an endothermic reaction, more energy is required to break the bonds of the reactants than is released when the products form.
• Chemical reactions can absorb several types of energy: electrical, light and thermal.
– Ex. Photosynthesis – plants absorb light energy from the Sun.
– Ex. Decomposition of water – electrical energy is needed to break water molecules into hydrogen and oxygen gas.
• In an endothermic reaction, the energy absorbed comes from the environment surrounding the reactants.
What are endothermic reactions?(cont.)
• Rate of reaction the measure of how fast a chemical reaction occurs.
• Chemical reactions occur faster if particles collide more often or move faster when they collide.
What can affect the rate of a chemical reaction?
• Surface area - Increased surface area increases reaction rate because more particles on the surface of a solid come into contact with the particles of another substance.
• Temperature - At higher temperatures, the average speed of particles is greater, particles collide more often, and collisions with more energy are more likely to break chemical bonds.
What can affect the rate of a chemical reaction? (cont)
• Concentration - Increasing the concentration of one or more reactants increases collisions between particles, resulting in a fast reaction rate.
• Pressure - In gases, an increase in pressure pushes gas particles closer together, resulting in more collisions.
What can affect the rate of a chemical reaction? (cont)
• Catalyst is a substance that speeds up a chemical reaction but is not used up itself or permanently changed.
– Ex. Enzymes – Are used by your body to speed up chemical reactions that convert food to fuel, store extra energy in fat and produce other enzymes.
What are catalysts?
A. endothermic
B. exothermic
C. single-replacement
D. decomposition
In which type of reaction is more energy released when the products form than is required to break the bonds in the reactants?
A. using an athletic cold pack
B. welding
C. iron rusting
D. burning wood
Which reaction is endothermic?
A. The substances melt faster.
B. More energy is needed to break the chemical bonds.
C. The bonds of the reactants do not require energy to break.
D. The substances have a greater surface area.
Which explains why reaction rates increase when the reactants are crushed?
Visual Summary
Chapter Review
Standardized Test Practice
During a chemical reaction, bonds are broken and atoms are rearranged to form new substances. Energy involved in chemical reactions is either stored in bonds or released.
• All matter is composed of tiny particles called atoms.
• The first model of the atoms was a solid sphere. Today’s model has a central nucleus with the protons and neutrons and an electron cloud surrounding it.
Lesson 1: Atoms
Lesson 2: Elements
• An element is a pure substance that cannot be broken down into any simpler substances. All atoms of the same element have the same number of protons.
• An element’s atomic number tells how many protons its atoms contain and its average atomic mass tells the average mass of its atoms.
• Elements are arranged on the periodic table according to their atomic numbers.
Lesson 3: Compounds
• Atoms of different elements can combine to form compounds.
• Ionic bonds usually involve the transfer of electrons from a metal atom to a nonmetal atom. A chemical bond that forms when atoms of nonmetals share electrons is called a covalent bond.
Lesson 4: Chemical Reactions and Energy
• In chemical reactions, energy is either absorbed or released. Energy is released in exothermic reactions. Energy is absorbed in endothermic reactions.
A. atom
B. electron
C. neutron
D. proton
Which term describes a neutral particle that exists in the nucleus of an atom?
A. Thomson
B. Rutherford
C. Chadwick
D. Bohr
Who discovered that, in addition to protons, the nucleus also contained neutrons?
A. reactants
B. products
C. elements
D. atoms
Which term refers to the substances produced by a chemical reaction?
A. polar molecule
B. covalent bond
C. chemical compound
D. none of these
Which of these describes a chemical bond formed when two atoms share one or more pairs of valence electrons?
A. positive ion
B. negative ion
C. isotope
D. quarks
Which describes an atom with a positive charge?
A. Increasing the surface area of the reactants.
B. Increasing the temperature of the liquids.
C. Increasing the concentration of the liquids.
D. Decreasing the temperature of the liquids.
All of these increase the rate of a chemical reaction between two liquids except
A. An electron in one atoms attracts a proton in another atom.
B. One atom takes an electron from another atom.
C. Two atoms share electrons and protons.
D. A neutron is transferred from one atom to another.
An ionic bond forms between atoms when
A. rubber
B. copper
C. gold
D. aluminum
Which would be best to use in making protective gear for an electrician?
A. atoms
B. electron clouds
C. protons
D. neutrons
The atomic number for an element indicates the number of
A. Nitrogen and oxygen
B. Oxygen
C. Carbon
D. Magnesium and sodium
What elements do laughing gas and rubbing alcohol have in common?
Compound Chemical
formula
Baking soda
NaHCO3
Table sugar
C12H22O11
Rubbing alcohol
C3H7OH
Milk of Magnesia
Mg(OH)2
Laughing gas
N2O
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