1. KEY CONCEPT All living things are based on atoms and their interactions.

2. An atom –smallest basic unit of matter
Contains:
a. nucleus has protons and neutrons.
b. electrons are in energy levels – regions around the nucleus.
Oxygen atom (O)
Nucleus: 8 protons (+) 8 neutrons
outermost energy level: 6 electrons (-)
inner energy level: 2 electrons (-)

6. Elements
Matter that has atoms that are all alike are elements.
Elements cannot be broken down into smaller substances.
Elements are listed on the Periodic Table.
More than 90% of the human body is made of only carbon, hydrogen, oxygen, and nitrogen.

7. Most abundant elements
The most common elements found in living things are Carbon, Hydrogen, Nitrogen, and Oxygen.
Oxygen, at 65%, is the element that makes up most mass in the human body.
Carbon follows with 18.5%, then hydrogen with 9.5%, and then nitrogen with 3.3%.

8. Living things consist of atoms of different elements.
An atom is the smallest basic unit of matter.
An element is one type of atom.
Hydrogen atom (H) H O
Oxygen atom (O)

9. O A compound is made of atoms of different elements bonded together.
water (H2O) O H _ +

10. A compound is made of atoms of different elements bonded together.
water (H2O)
carbon dioxide (CO2)
Glucose

11. An ion forms when an atom gains or loses one or more electrons.
positive ions -formed when atoms lose electrons
negative ions -formed when atoms gain electrons
Ionic bonds –chemical force due to electircal attraction between oppositely charged ions.
Sodium atom (Na)
Chlorine atom (CI)
Sodium ion (Na+)
Chloride ion (CI-)
Na loses an electron to CI
ionic bond
gained electron

13. Molecules- atoms bonded together by covalent bonds
Covalent bonds form when atoms SHARE electrons in their outer energy level. This allows both atoms to become full and stable.
covalent bonds
Oxygen atom (O)
Carbon atom (C)
Carbon dioxide (CO2 )

14. Covalent bonds
Most organic (coming from living things) compounds have covalent bonds.
This includes sugars, fats, proteins, and water.

17. Compounds you need to know:
H2O = water
CO2 = carbon dioxide
C6H12O6 = sugar (usually glucose)
NaCl = table salt
NH3 = ammonia

18. Isotopes
Atoms with the same number of protons and electrons but different numbers of neutrons are called isotopes.
Isotopes have the same element, but may have different properties because of their different masses that may change its stability.
Isotopes are named by adding the number of protons and neutrons.
Some isotopes are useful in telling the age of fossils.