Chapter 8.2 - Compounds, Chemical Formulas, and Covalent Bonds – p275-282 - page1

Vocabulary

• Covalent Bond (277) – a chemical bond formed when two atoms share one or more pairs of valence electrons

• Molecule (278) – a group of atoms held together by covalent bonding that acts as a n independent unit

• Polar Molecule (279) – A molecule that has a partial positive end and a partial negative end because of unequal sharing of electrons

• Chemical Formula (280) – a group of chemical symbols and numbers that represent that elements and the number of atoms of each element that make up a compound Review

• Compounds are substances made up of two of more different ________________

• Compounds and the elements that make them up often have different properties

• Chemical _____________ join atoms together.

• One way atoms from bonds is by sharing ____________ electrons

Covalent Bonds – Sharing Electrons

• When unstable, nonmetal atoms bond together, they bond by ______________ valence electrons.

• A covalent bond is a chemical bond formed when two atoms share one or more ____________ of valence electrons.

• The atoms then form a ___________ covalent compound A Noble Gas Electron Arrangement

• An atom with less than eight valence electrons becomes stable by forming chemical bonds until it has ________________ valence electrons.

• The most chemically stable state for most atoms has the electron configuration of a ________________________.

• Look at H2O H2O Bonding

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Shared Electrons • If the oxygen atom and each hydrogen atom share their _______________ valence electrons,

they can form two covalent bonds and become a stable covalent compound. • Each covalent bond contains _____________ valence electrons. • Since these electrons are shared, they count as valence electrons for ______________

atoms in the bond. • In H2O, all three atoms combine sharing valence electrons. We know the compound is

stable because all ________________ atoms have eight valence electrons. Double and Triple Covalent Bonds

• A single covalent bond exists when two atoms share ___________ pair of valence electrons.

• Double bonds exist when two atoms share _________ pairs of valence electrons.

– Double bonds are ____________ than single bonds

• Triple covalent bonds exist when two atoms share ____________ pairs of valence electrons.

– Triple bonds are stronger than ___________ bonds.

Covalent Compounds

• Covalent compounds usually have __________ melting points and low boiling points.

• They are usually gases or liquids at ________________temperature, but they can also be solids

• Covalent compounds are _______________ conductors of thermal energy and electricity Molecules

• A molecule is a group of atoms held together by covalent boning that acts as an independent unit,

• Table sugar (C12H22O11) is a __________________ compound.

• One grain of sugar is made up of _________________ of sugar molecules.

• One molecule of sugar contains _________carbon atoms, ___________hydrogen atoms, and __________oxygen atoms.

• The only way to break a molecule of sugar would be to chemically separate the atoms of C, H, and O.

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Water and Other Polar Molecules • In a covalent bond, one atom can __________________ the shared electrons more strongly

than the other atoms can. • Consider H2O

– The _________________ atom attracts the shared electrons more strongly than each hydrogen atom does.

– As a result, the shared electrons are pulled ______________ to the oxygen atom.

– Since electrons have a negative charge, the oxygen atom has a partial ___________________ charge.

• A molecule that has a partial positive end and a partial negative end because of unequal sharing of electrons is a ________________molecule.

Dissolving Molecules • The charges on a polar molecule affect its properties. • Sugar dissolves easily in water because sugar and water are____________________ . • The negative ends of a ____________________ molecule pulls on the positive end of a sugar

molecule. • Also, the positive end of a water molecule pulls on the negative end of the sugar molecule. • This causes the sugar molecules to ___________________ from one another and mix with

the water molecules.

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Nonpolar molecules • A hydrogen molecule, H2, is a __________________ molecule. • Hydrogen atoms are identical, their attraction for a shared electron is equal. • The carbon dioxide molecule, CO2, is also________________________. • A nonpolar compound will not easily dissolve in a polar compound, but it will dissolve easily

in a nonpolar compound. • Oil is an example of a nonpolar compound. It will

not dissolve in_____________________. Chemical Formulas and Molecular Models • A chemical ___________________ is a group of chemical symbols and numbers that

represent the elements and the number of atoms of each element that make up a compound.

• Just as a recipe lists ingredients, a chemical formula lists the elements in a compound. • For example, the chemical formula for carbon dioxide is CO2.

– CO2 is made up of carbon and _______________ atoms. – The____________________ , or small number after a chemical symbol, shows the

number of atoms of each element in the compound. – CO2 contains _______ atoms of oxygen bonded to ________ atom of carbon.

• When parentheses (“()”) are used, any subscript applies to all the elements inside the parentheses.

Example: Al2(SO4)3 _____ Aluminum _____ Sulfur _____ Oxygen

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Counting Atoms

Name each of the following chemical compounds and determine how many atoms of each element are present: 1) CaF2 ___1 Calcium, 2 Flourine_________________________________ 2) Be(OH)2 ____________________________________________________ 3) NO2 ______________________________________________________ 4) Al2(SO4)3 ___________________________________________________ 5) NH4NO3 ____________________________________________________ 6) S2F2 ______________________________________________________ 7) Na2CO3 ____________________________________________________ 8) CH4 ______________________________________________________