Chapter 2: Matter

Section 2: Combining Atoms

A. Interactions of Atoms

1. There are about 90 naturally occurring elements on Earth.

a. These elements can combine countless ways.

2. Examples: Hydrogen and Oxygen can combine many ways!!!

a. Hydrogen (H): elemental gas (Explosive)

b. Oxygen (O): elemental gas (Needed for combustion)

c. Water: H20 (Puts out fires!!!)

d. H202 Hydrogen Peroxide (Antiseptic & bleach)

B. Compounds 1. Compound : contains more than one type of

element that are CHEMICALLY bonded together. a. Form a new substance during chemical changes only.

b. Atoms rearrange positions

c. Changes depend on chemical activity.

d. Based on electrons in outer shell.

e. Atoms will always try to form stable bonds.

f. Impossible to be separated by physical means.

2. Compound properties differ from the elements making it up!!

3. Elements always combine in a specific ratio: a. CO= Carbon Monoxide (1:1)

b. CO2= Carbon Dioxide (1:2)

C. Chemical Properties

1. A property that describes a change that occurs when one substance reacts with another substance is called a CHEMICAL PROPERTY.

2. Example:

a. Iron reacting with water to form rust.

b. Rust= Iron Oxide

3. Example 2:

a. Iron mixed with chromium and nickel in stainless steel will not rust!!!

D. Bonding 1. Forces that hold atoms together in compounds

are called chemical bonds. a. Formed when atoms share or exchange electrons.

b. Only electrons having the highest energies in the electron cloud can form bonds. (farthest from the nucleus)

2. Rule of 8 a. Atoms always try to form stable outer shells of 8

electrons.

b. If an atom has fewer than 8 in the outermost level, it is unstable and is more likely to combine with other atoms.

c. Full shells or 8 electrons in the outermost shell makes atoms happy!!!!

E. Covalent Bonds

1. Covalent Bond: the sharing of electrons in the outermost energy level.

2. Covalent bonds always

form MOLECULES.

3. The sharing of the electrons in figure 7 gives both hydrogen and oxygen full outer shells.

4. See pg 41 of your online text.

F. Ionic Bonds

1. Ionic bond: combining of a positive and negative charged ion.

a. Ion: Electrically charged atoms.

2. Atoms can be neutral, or under certain conditions, atoms can lose or gain electrons.

a. Lose an electron= positive charged atom.

b. Gain an Electron= negative charged atom.

3. Ions of opposite charges are attracted to each other.

a. Just like magnets: opposites attract; like charges repel.

Ionic Bonding in School!!!!

G. Metallic Bonds

1. Found in metals such as copper, gold, aluminum, and silver.

a. Electrons are free to move from one positively charged ion to another.

b. Free movement of electrons, or conductivity, allows metals like copper to pass an electric current easily.

H. Hydrogen bonds

1. Hydrogen bonds can from without the interaction of electrons.

a. Polar Molecule: molecule with a positive and negative end. (like water) 1. This occurs because the atoms do not share electrons equally.

2. Hydrogen atoms produce a positive charge; oxygen produces a negative charge.

2. Hydrogen bonds are responsible for several properties of water.

a. Cohesion: the attraction between water molecules that allows them to from raindrops and to form beads on flat surfaces.

b. Cause water to exist as a liquid, rather than a gas, at room temperature.

c. As water freezes, hydrogen bonds force water molecules apart, into a structure that is less dense than liquid water.

I. Chemical Formulas

1. Chemical formula : a group of symbols that represent a compound.

a. Shows elements along with ratios.

b. The small “2” is called a subscript.

1. The subscript shows how many atoms of each element combine to form a compound.

2. If there is no subscript there is only 1 atom of that element.

2. Example: CO2

a. 1 atom of carbon.

b. 2 atoms of oxygen.

J. Naming Binary Compounds

1. Binary Compound: a two element compound.

a. Name of the positive ion (metal) is always written first.

b. The negative ion name is changed to end in “ide”.

2. Examples:

a. HCl= Hydrogen Chloride

b. KBr= Potassium Bromide

c. NaCl= Sodium Chloride

d. KI= Potassium Iodide.

K. Substances

1. Elements and compounds are substances because they have definite composition.

L. What is a Mixture?

1. When two or more substances are not chemically combined.

2. Mixtures do not have specific ratios.

a. Example: Iced Tea (Tea mix, sugar, water)

3. Two types of mixtures: heterogeneous and homogeneous.

M. Heterogeneous Mixture

1. Components are not mixed evenly and each component retains its own properties.

2. Examples of heterogeneous mixtures

a. Salad Dressing.

b. Rock in Figure 11

3. Particles are 1000 nm or bigger. (dirt, sand, pebbles)

4. Particles can be seen with a microscope or unaided eye.

5. Particles will settle out over time. (by gravity_ a. Ex: Italian salad dressing, pebbles in water.

N. Homogeneous Mixtures 1. Mixtures that are evenly mixed throughout.

a. You cannot see the individual components.

b. Also called a SOLUTION if it is dissolved in a liquid.

2. Solutions a. Particles do not settle out.

b. Particles cannot be filtered out.

c. Particles must be dissolved

d. Particles very small (.1 to 1 nanometer)

3. Examples of solutions a. Iced Tea

b. Sea Water

c. Soda

O. Separating Mixtures

1. Components can be separated by physical means.

a. Example: pick out all of the blue pens in a mixture of pens.

2. Substances in a compound CANNOT be separated by physical means.