The Structure of Atoms and the
Periodic Table
Review of notes and Chapter 5
Atoms – The building blocks of all matter
Protons and neutrons are in the nucleus
electrons are orbiting about in various orbitals or energy levels
Protons have a positive electrical charge
Neutrons have no electrical charge and
Electrons have a negative electrical charge
Particle charges and attractions
Atoms have many combinations of protons, neutrons, and
electrons
An Element is defined by
the number of protons
contained in the nucleus.
Each electron oribital or energy level can hold only so many electrons
The electrons fill the lowest energy level first then the higher levels.
Copper atom with electron energy levels
What period is this element in?
Electron cloud orbital shapes
Electron configuration
How electrons fill orbital shell
Energy levels with maximum number
of electrons
Remember the first 2 energy levels and the
Duet and Octet rule
Isotopes – variations of an element
The same number of protons
but a different number of neutrons
the atomic number stays the same
and mass number changes
Each element has a Name, Symbol,
Atomic Number, and Atomic Mass Number
Atomic number – the number of protons
Mass number – number of protons and neutrons
What is the atomic number?
What is the atomic mass number?
What is this element?
What about this one?
Chemical reactions take place and compounds form when atoms
stick together by overlapping electron clouds.
2 hydrogens and 1 oxygen come bond
to make 1 water molecule
Atoms want a complete outer shell and will
share or transfer electrons to do so.
Ions are formed when electrons are lost or gained
Ions are electrically charged particles
Cations have lost electrons and are positively charged
Anions have gained electrons and are negatively charged.
The Periodic Table of the elements
An organized way to present the elements
There are 18 columns or groups – groups have similar properties
There are 7 rows or periods – periods do not have similar properties
The period number is the number of energy levels the element in it has
Periodic Table Groups
Group 1 The Alkali Metals – highly reactive metals, explodes on contact with water
Group 2 The Alkali Earth Metals - reactive and lightweight, some important to diet
Groups 3-12 The transition Metals – not very reactive, easily shaped, used for coins, buildings,
jewelry, and usually good conductors of electricity
Group 17 The Halogens – highly reactive nonmetals, forms salts, used to kill microorganisms
Group 18 The Nobel Gases – rarely reacts with other elements (last to be found), used in lights
Some elements change identity
through radioactive decay.
• When the nucleus is unstable because it has
too many or too few neutrons it may decay by
emitting a proton or neutron.
• If a proton is emitted then the element
changes into another element
• All elements with atomic number of 92 and
higher are radioactive
Radioactive decay
A Half-life is the amount of time for half of the
sample to decay
Decay of Strontium
The half-life is 25 years, the amount of time for 50 g or half of the sample to decay.
Can you find how much of the sample is left after 3 half-lifes? How about 4? 5?
Scientists use the decay of the isotope Carbon 14 to
date artifacts and remains of plants animals
Carbon 14 has a mass of 14, it has 2 more neutrons than Carbon 12