The Atom

Consider Russian nesting dolls (matryoshka dolls). Each one is smaller than the one before it. If each doll is ½ the height of the one before it, how many would it take to make a stack 3 feet tall?

How many times can you divide a block of wood in half? What do you get each time? At the “end?”

• At some point, you cannot divide that block any more without changing its properties as wood.

• Even further on, you cannot divide the molecule without breaking it into its atoms.

Atoms• Atoms are the fundamental building blocks of

all matter.• Atoms have distinct properties and combine

with each other based on these.• These properties come from each atom’s

makeup of PROTONS, NEUTRONS, and ELECTRONS.

Protons• Each atom contains a set number of protons.• Protons carry a positive charge• Each proton has a mass – a very small mass.– A mass so small we measure it in atomic mass

units (amu).– Protons have a mass of 1 amu.

• As a side note, the number of PROTONS in the nucleus is the ONLY thing that decides what kind of atom you’re looking at.– 6 protons, 8 neutrons– 8 protons– 12 electrons• AHA! Sometimes this doesn’t work!

Neutrons

• Neutrons, along with protons, are found in the atom’s core – the nucleus.

• Neutrons have a neutral charge (no charge).• Neutrons are just as heavy as protons. We

measure their mass in atomic mass units (amu).– They have a mass of 1 amu.

The Nucleus

• The nucleus is the solid core of every atom, and contains essentially ALL of the atom’s mass.

Electrons• Electrons are the negatively-charged particle

of the atom• They have a charge of -1• BUT! They have very little mass. • We consider this mass to be 0 amu.

• Electrons are found in a “cloud” around the atom.

The Cloud

The Cloud (cont’d)

• BUT! Electrons have distinct energy levels within that cloud.

• We won’t worry about this just yet, but know that there is some order to the way these electrons are organized.

• Atoms interact with each other to form bonds.– Electrons do all the interacting.

• Of all the electrons, only those in the highest energy levels participate in bonding. We’ll talk more on this later.

• There are 3 different kinds of bonds– Ionic bonds– Covalent bonds– Metallic bonds

• Bonds hold atoms together to form ELEMENTS and COMPOUNDS.

Elements• Compounds which are made up of only one

type of atom are called ELEMENTS.• Atoms have the properties of their element.• Examples of these would be copper (Cu),

aluminum (Al), silver (Ag), hydrogen (H), etc.• Pure metals use metallic bonds to share

electrons.

Compounds• Compounds are substances that are formed

when two or more different elements bond.• Compounds can display ionic or covalent

bonds.– Ionic bonds come from an unequal sharing of the

electrons.– Covalent bonds come from an equal sharing of the

electrons.

Molecules

• Molecules may be made up of several kinds of atoms.

• A MOLECULE is the smallest unit that maintains the properties of a compound.

• Molecules have entirely different properties than those of the parent atoms.

Sodium is a highly reactive metal. So much so, that it needs to be kept in oil, because it would react with oxygen and water in the air otherwise.

Chlorine gas is used as a chemical weapon in some places. It is highly toxic (although, people who described its scent generally described it somewhere between pepper and pineapples).

How many of you think the cafeteria food here is always perfect just the way it is?

What would you do if you wanted to flavor it?

…Yep. Salt.

Practice

Compound, element, or molecule?• H2O

• Baking soda (NaHCO3)• Copper• Gold• HCl• CO2

• Starch

Which element is it?

1. Grab an egg.2. Open the egg.3. DO NOT EAT THE CANDY YET!4. Determine the element.5. ????6. Profit!

Fill in the chart

Element # Protons # Neutrons # Electrons Mass # Atomic #

Hydrogen 1 1 Carbon 6 12 7 14 7 4 9 4 20 23 9 10 11 23