CHAPTER 8Section 2- Compounds, Chemical Formulas, and Covalent bonds

COMPOUNDS

Compounds- a substance made up of two or more elements

The compound has different properties from the elements that make up the compound

Ex- NaCl- common table salt Na- Is a bright, soft metal when it is purifies Cl- is a gas at room temperature However, when combined they make a

compound that is used as a seasoning for foods.

CHEMICAL BONDS

A chemical bond is a force that joins atoms together

Bonds can be formed in two ways Sharing electrons (Covalent bonds) Giving/Receiving electrons (Ionic Bonds)

COVALENT BOND

A covalent bond is a chemical bond formed when two atoms share one or more pairs of valence electrons Generally non metals form these kinds of bonds Each element in the bond wants to reach noble

gas status Each element wants to share electrons so that

each has 8

NUMBERS OF COVALENT BONDS

A single covalent bond occurs when two atoms share one pair of valence electrons

A double covalent bond occurs when two atoms share two pairs of valence electrons

A triple covalent bond occurs when two atoms share three pairs of covalent bonds Strength of bonds Strongest- Triple Weakest-Single

COVALENT COMPOUNDS

The bonds in water, carbon dioxide, and sugar are very different but they do have some similarities Low melting and boiling points Usually gases or liquids at room temperature Poor conductors of thermal energy and electricity

MOLECULES

The chemically stable unit of a covalent compound is a molecule

A molecule- is a group of atoms held together by covalent bonding that acts as a single or independent unit

For example- Table sugar is C₁₂H₂₂O₁₁ One grain of sugar is made up of millions of sugar molecules One molecule would be made up of 12 Carbon atoms, 22

Hydrogen atoms, and 11 Oxygen atoms

WATER AND OTHER POLAR MOLECULES

In a covalent bond, one atom can attract the other atom more strongly

For example, in water the Oxygen attracts the Hydrogen more

The Oxygen is more negative and has a partial negative charge

The Hydrogen has a partial positive charge A molecule that has a partial negative and a

partial positive charge because of unequal sharing of electrons is POLAR COVALENT

NONPOLAR MOLECULES

Usually occurs when the same atom is bonded with itself

Also occurs when the electrons are shared equally

Non polar compounds dissolve easily in other non polar compounds but not so well in polar compounds

“Like dissolves like”

CHEMICAL FORMULAS AND MOLECULAR MODELS

A chemical formula is a group of chemical symbols and numbers that represent elements and the number of atoms of each element.

“like a recipe” CO₂ means one atom of carbon and 2 atoms of oxygen The subscripts shows the quantity of the element The formula DOES NOT SHOW THE SHAPE OF THE

MOLECULE