• 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