Atoms, Elements, and Molecules
Atoms
• Atoms are the building blocks of matter.
• They make up everything that we know.
• All matter is made of atoms.
• Made up of three smaller parts.
– Protons
– Neutrons
– Electrons
Atoms
Nucleus
8 Protons
8 Neutrons
Oxygen
Atoms
Electrons
Atomic Shell
Elements
• Matter made of only one type of atom is
called an element.
Element Name
Atomic Number
Element Symbol
Mass Number
Elements
• Atomic Number: The number of protons in
the nucleus of an atom.
• Mass Number: The number of protons and
neutrons in the nucleus.
Elements: Substances made entirely
from one type of atom.
Molecules
• A molecule is formed when two or more
atoms join together chemically.
Molecular
Oxygen
O2
H2O Water
Methane
CH4
Compounds
• A compound is a molecule that contains at
least two different elements.
• All compounds are molecules not but not all
molecules are compounds.
Molecular
Oxygen
O2
H2O Water
Methane
CH4
Challenge: Covalent Bonding
• What you need to know:
– The elements on the periodic table have the same
number of protons and electrons.
– Covalent bonds share electrons to fill an atoms
valence shell.
– Valence Shells
• Holds the electrons of an atom.
• Octet Rule: An atom is most stable when its outermost
shell is filled with electrons.
Challenge
Number of electrons = 2n
2
n = shell number
Challenge: CO2