2.1 Atoms, Ions, and Molecules
KEY CONCEPT
All living things are based on atoms and their
interactions.
2.1 Atoms, Ions, and Molecules
• 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 (-)
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.
Hydrogen atom (H)
H
Oxygen atom (O)
O
2.1 Atoms, Ions, and Molecules
• A compound is made of atoms of different elements
bonded together.
– water (H2O)
_
O
H
+
H
+
2.1 Atoms, Ions, and Molecules
• A compound is made of atoms of different elements
bonded together.
– water (H2O)
– carbon dioxide (CO2)
– Glucose
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.
gained electron
Na loses an
electron to CI
Sodium atom (Na)
Chlorine atom (CI)
ionic bond
Sodium ion (Na+)
Chloride ion (CI-)
2.1 Atoms, Ions, and Molecules
2.1 Atoms, Ions, and Molecules
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 )
Oxygen atom (O)
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.