Elements

• It has to be on the Periodic Table.

• Elements are “pure” meaning they cannot be broken down chemically.

Periodic Table

• period

• group

• Group 1: alkalis

• Group 17: halogens

• Group 18: Noble Gases

Atomic Math

• Atomic number = the number of protons

• Atomic mass = # of protons + # of neutronso So # neutrons =?

Element vs. Compound• Elements• found in nature

• is on the Periodic Table of the Elements

• contains only 1 element

• some needed for life

• smallest part of an element is an atom

• Examples: carbon, oxygen, iron

• Compounds• found in nature

• has 2 or more elements

• some needed for life

• smallest part of a compound is a molecule

• created by a chemical reaction

• Examples: water, carbon dioxide

Examples of Chemical Properties

• flammability (it can burn)

• reactivity to oxygen (corrosion)

• reactivity to light

• reactivity to water

• reactivity to electricity

• reactivity to acid

Signs of a Chemical Change• releasing a gas, bubbling• a change in temperature• forming a precipitate (a solid)• a change in color• reacting with oxygen (burning or rusting)• giving off light• making a noise (explosion)• not reversible

Law of Conservation of Mass

• Says the total mass before the reaction is the same as the total mass afterwards.

• No matter is created or destroyed in a chemical reaction!

Drawing an Atom!• The atomic number = # of protons = # of electrons• The atomic mass = total # of protons and neutrons in nucleus.• Step 1: Find the atomic mass for your element. Draw that many

circles for your nucleus. Pack them close together!• Step 2: Find the atomic # for your element. Color that many

circles for your protons. Spread them around the entire nucleus.

• Step 3: Color the rest of your nucleus as neutrons.• Step 4: Draw the electrons around the nucleus, completely

surrounding it. The number is the same as the number of protons.