South Pontotoc Biology: Unit 4

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: