Substances react chemically in characteristic ways with other substances to form new substances (compounds) with different characteristic properties. In chemical reactions, the total mass is conserved.
Unit Essential Question(s):
How do chemical reactions reflect the law of conservation of mass?
Discuss how atoms can join together with chemical bonds to form molecules.
Recognize two types of chemical bonds (ionic and covalent) which result from the shifting of valence electrons. Use a bohr model to illustrate that the valence electrons are the electrons in the outermost shell of an atom.
Discuss how the chemical bonds that join atoms together to form molecules and compounds are the result of attractive forces between the atoms. Explain how atoms are more stable when their outer shell is filled, they tend to lose, gain, or share electrons to complete their outer shell.
LEQ Number 2
Describe how ionic bonds are formed when electrons transfer from one atom to another.
Explain that when an atom loses an electron it becomes a positively charged ion (cation). The positive ion is usually a metal. When an atom gains an electron it becomes a negatively charged ion (anion). The negative ion is usually a nonmetal.
Recognize when two ions have opposite charges they attract to each other.
Show examples of ionic bonds.
Describe how covalent bonds are formed by sharing electrons. The sharing of valence electrons in covalent bonding is the result of both atoms "fighting" for the electrons, with neither one "winning." Covalent bonds form between two nonmetals.
Recognize that covalent bonds can be formed with one or more pairs of electrons. A single bond is the sharing of one electron pair. It is also common to have double bonds (two pairs of electrons shared between the atoms) and triple bonds (three pairs of electrons shared between the atoms).
Show examples of covalent bonds.
LEQ: Number 3
HOTS: Comparing/Contrasting, Inductive Reasoning or Error Analysis could be used to demonstrate the ET LEQ.
Discuss the properties of compounds: the relative proportions of the elements in a compound are fixed, the components of a compound do not retain their individual properties and large inputs of energy are required to separate the components of a compound.
Explain that a chemical change occurs when a compound is formed.
Discuss how compounds fall into three categories: neutral, acidic or basic (alkaline).
Describe the characteristics of acidic and alkaline substances and give examples of each using a pH scale. Emphasize that an acid is a substance that donates hydrogen ions. A base is a substance that accepts hydrogen ions.
Use a pH indicator to investigate the characteristics of acids and bases.
Discuss how the combination of an acid and base in proper amounts can produce a neutral substance.
LEQ: Number 2
Recognize that many chemical compounds may be classified as salts such as sodium chloride (table salt), sodium bicarbonate (baking soda) and magnesium sulfate (epson salt). Salts are ionic compounds that are composed of metallic ions and nonmetallic ions.
Explain that when acids and bases react with each other, they can form a salt and water. This is called a neutralization reaction. The reverse of the neutralization reaction is called hydrolysis. In a hydrolysis reaction, a salt reacts with water to yield the acid or base.
LEQ: Number 3
HOTS: Comparing/Contrasting, Classifying/Categorizing or Error Analysis could be used to demonstrate the ET LEQ.
Recognize that chemical changes are also called chemical reactions. Chemical reactions involve combining different substances. The chemical reaction produces a new substance with new and different physical and chemical properties.
Explain that a chemical change occurs whenever there is a rearrangement of atoms that makes or breaks chemical bonds.
Discuss how chemical reactions usually liberate or absorb heat. When heat is given off in a chemical change or reaction, it is called an exothermic reaction. When heat is absorbed in a chemical change or reaction, it is called an endothermic reaction.
Investigate how temperature influences chemical changes.
Discuss other signs of chemical changes such as color change, production of a gas, formation of a precipitate, emission of light and odor change.
Show examples of chemical reactions using chemical formulas. Students do not need to learn how to write chemical formulas or balance chemical equations.
Recognize that sometimes substances called catalysts are used to speed up or help along a chemical reaction.
LEQ: Number 2
Discuss how in chemical reactions the number of atoms stays the same no matter how they are arranged, so the total mass stays the same. Matter is never destroyed or created in chemical reactions. The particles of one substance are rearranged to form a new substance. The same number of particles that exist before the reaction exist after the reaction.
Demonstrate balancing chemical equations to illustrate the law of conservation of matter. Students do not need to learn how to write chemical formulas or balance chemical equations.