10/3/14

Objective: What are elements, compounds, and atoms?

Do Now: Give an example of “matter.”

Chapter 4: The Chemical Basis of Life

Matter: Anything that occupies space and has mass

Element: Pure substance that cannot be broken down into other substances

Ex: Carbon (C), Hydrogen (H), Gold (Au)4 most common elements in living matter (96% of our body):

carbon (C), oxygen (O), hydrogen (H), nitrogen (N)

Trace Element: elements that make up less than 0.01 percent of your body, but are critical to life

Ex: iron

Compound: 2 or more elements chemically combined

Ex. Carbon dioxide(CO2), water(H2O)

Atomsatom: smallest possible particle

of an elementMade up of :Nucleus: central core of atom that contains

protons: single unit of positive electrical charge (+) neutrons: electrically neutral = no charge

Electrons: single unit of negative electrical charge (-) located outside of the nucleus

Why do you think the electrons remain close to the nucleus?

Atomic number: number of protons in an atom– Differentiates elements

Carbon Potassium

Atomic Weight (Mass number): # of protons + # of neutrons

Isotopes

• Isotope: same number of protons but different number of neutrons– Can make an element

radioactive– ex: 12C = normal, 14C

=radioactive

• Radioactive Isotope: nucleus decays over time giving off radiation in the form of matter and energy– ex. Carbon dating

Energy Levels• The electrons in an atom

determine how it will react with other atoms

• Electrons are found in clouds outside the nucleus

• Energy Levels– First level = lowest, nearest to

nucleus can hold 2 electrons– Second level = can hold 8

electrons– Most reactive when they have

partially full energy levels Nitrogen

Chemically reactive or Inert (doesn’t react)?