2.1 Atoms, Ions, and Molecules

KEY CONCEPTAll living things are based on atoms and their interactions.

2.1 Atoms, Ions, and Molecules

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 (-)

• An atom –smallest basic unit of matter

2.1 Atoms, Ions, and Molecules

2.1 Atoms, Ions, and Molecules

2.1 Atoms, Ions, and Molecules

2.1 Atoms, Ions, and Molecules

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.

2.1 Atoms, Ions, and Molecules

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%.

2.1 Atoms, Ions, and Molecules

Living things consist of atoms of different elements.

• An atom is the smallest basic unit of matter.• An element is one type of atom.

H

O

Hydrogen atom (H)

Oxygen atom (O)

2.1 Atoms, Ions, and Molecules

– water (H2O)

OHH

_

++

• A compound is made of atoms of different elements bonded together.

2.1 Atoms, Ions, and Molecules

– carbon dioxide (CO2)

– Glucose

• A compound is made of atoms of different elements bonded together.

– water (H2O)

2.1 Atoms, Ions, and Molecules

• 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 anelectron to CI ionic bond

gained electron

2.1 Atoms, Ions, and Molecules

2.1 Atoms, Ions, and Molecules

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) Oxygen atom (O)

Carbon dioxide (CO2 )

Molecules- atoms bonded together by covalent bonds

2.1 Atoms, Ions, and Molecules

Covalent bonds

• Most organic (coming from living things) compounds have covalent bonds.

• This includes sugars, fats, proteins, and water.

2.1 Atoms, Ions, and Molecules

2.1 Atoms, Ions, and Molecules

2.1 Atoms, Ions, and Molecules

Compounds you need to know:

H2O = water

CO2 = carbon dioxide

C6H12O6 = sugar (usually glucose)

NaCl = table salt

NH3 = ammonia

2.1 Atoms, Ions, and Molecules

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.