Review of the Atom

Key Words subatomic particle energy levels Atomic mass proton electronneutron atomic mass unit (u)atomic number

Atoms can be broken down into subatomic particles. ATOMS AND ELEMENTS Elements are pure substances containing one type of atom. The atom is the smallest part that retains all the properties of that element.

The modern atomic theory states that an atom consists of three subatomic particles: protons neutrons electrons

Neutrons Protons A proton has a mass of 1 atomic mass unit (μ). Since the neutron is the same size, it is also 1 μ. electrons Electrons are considered zero mass (too small). All unreacted atoms are neutral - number of protons and electrons are the same. + -

The atomic mass is equal to the total mass of the protons and neutrons in the nucleus The units of Atomic mass are amu OR μ.

Heavier elements have a bigger nucleus – more protons (and neutrons). No TWO elements have the same number of protons.

Number of protons in an element does NOT change. Proton number is used to identify an element. The number of protons in the nucleus of an element is called the atomic number.

Number of ProtonsAtomic Number Number of NeutronsAtomic Mass – Atomic Number Number of ElectronsNumber of protons (Atomic Number) 4 – 2 = 2

Gold – How many protons are there in one atom of gold? Atomic number is 79 – 79 p + How many electrons are there in one atom of gold? How many neutrons are there in one atom of gold? How many protons are there in 10 atoms of gold? Atoms are neutral – 79 e - At mass – At number 197 – 79 = 118 n 0 10 x 79 p + = 790 p + atomic number (79) atomic mass (197u)

Atom is made of protons, neutrons and electrons. Electrons travel in orbits or energy levels around the nucleus. Atomic number is equal to the number of protons. Atoms are neutral - number of protons and electrons is the same. Atomic mass is the protons plus the neutrons