Basic Chemistry Study Guide

Be able to do the following:

1. Identify the number of protons, neutrons, and electrons, and the atomic number and atomic mass for certain elements:
For example: Helium has:

• Atomic number of 2
• Atomic mass of 4
• 2 Protons (atomic number)
• 2 Electrons (equal to the number of protons in neutral atoms)
• 2 Neutrons (Subtract atomic number from atomic mass: 4-2=2)

2. Draw the Bohr diagram for certain elements:
For example: Aluminum has an atomic number of 13, so it has 13 protons and 13 electrons
The rules for drawing the electrons are:

• the energy level (shell/orbit) closest to the nucleus can hold up to 2 electrons, fill it up first
• the next energy level can hold up to 8 electrons, fill it up next
• the next energy level can hold up to 18 electrons, fill it up next
• Aluminum has 2 in the first energy level, 8 in the second energy level, and 3 in the third energy level for a total of 13electrons

3. Draw the Electron Dot Diagram (Lewis Structure) for certain elements:
For example Chlorine
The rules for drawing the electrons

• Determine the number of valence electrons (electrons found on the last energy level) an element has by looking at the column that it is in
• Draw dots representing electrons around the elements symbol, beginning with the right side and continuing counterclockwise
• Draw one dot per side until you return to the right side
•  Then draw another dot
• Make sure the dots line up two to each side of the symbol
• No element has more than 8 valance electrons

4. Determine if a molecule is bonded with Ionic or Covalent bonds:
For Example NaCl (sodium chloride)
The rules for determining what kind of bond elements have

• metals bonded with other metals make a metallic bond
• Metals bonded with Non-metals make an Ionic Bond
• Non-metals bonded with Non-metals make Covalent bond
• Na is a metal and Cl is a non-metal so they have an Ionic bond 

Remember:
In Ionic bonds

• Metals are bonded to non-metals
• Atoms transfer electrons to other atoms
• This give the atoms a charge and it becomes an ion
• This charge causes the atoms to become attracted to each other
• Sodium gives an electron to Chlorine
• Sodium becomes positively charged
• Chlorine becomes negatively charged
• The two opposites are attracted to each other and form table salt (sodium chloride)

In Covalent Bonds

• Non-metals are bonded with other non-metals
• Atoms share electrons with each other
• Hydrogen shares its only electron with Chlorine
• Chlorine shares one of its electrons with Hydrogen

5. An ion is an element that has lost or gained electrons.

• If an element loses an electron, it has more protons than electrons so it becomes positively charged (cation).
• If an element gains electrons, it has more electrons than protons so it becomes negatively charged (anion).
• Sodium loses its outer electron and becomes positively charged.

6. An isotope is an element that has more or less neutrons.
For example Carbon:

• Carbon has 6 protons, 6 electrons, and usually 6 neutrons if its mass is 12.
• If Carbon gains one neutron, its mass increases from 12 to 13, and it is an isotope called Carbon-13.
• If Carbon gains two neutrons, its mass increases from 12 to 14, and it is an isotope called Carbon-14.
• Note that the number of protons and the number of electrons did not change.

7. General notes to remember:

• The atomic mass of an element is the sum of its protons and neutrons.
• Isotopes are elements that have a different number or neutrons; the number of protons and electrons did not change.
• Ions are elements that have a charge because they lost or gained electron; the number of protons and neutrons did not change.

Bohr Diagrams for the first 20 elements:

Electron Dot Diagrams for the first 20 elements: