1. Atoms

2. What are atoms? • The basic building blocks of matter • They make up everything found in the world around us. • You are even made up of atoms! • Atoms are made up of three subatomic particles: • Protons • Neutrons • Electrons • Each of these particles carries a charge • Take a moment to think about what charge you believe each of these particles carry.

3. Protons and Neutrons • Protons carry a positive charge • Neutrons carry a neutral (no) charge • The nucleus of the atom is made up of a mass of protons and neutrons

4. Electrons • Carry a negative charge • Circle the nucleus forming the electron cloud • Very small compared to the other parts of the atom and move so fast it is difficult to pinpoint their location

5. Balance • The number of protons and electrons in an atom are usually equal • This causes the atom to have a neutral (no) charge • What would happen if there were more electrons than protons? • More protons that electrons?

6. Valence Electrons • The electrons in the outermost shell of an atom • This shell is called the valence shell • The only electrons that react with other atoms

7. How to find the valence electrons • Take out the copy of the periodic table and a pencil • Number the columns of the periodic table • Not including the ten columns of the transition metals in the middle block • Starting from the left label the first column 1, the second column 2, the thirteenth column 3, the fourteenth column 4…until you are to the right side of the table and you have labeled the eighteenth column 8

8. 1 2 3 4 5 6 7 8 * *except He (it has 2 valence electrons)

9. How to find the valence electrons • The number that you have put above the column represents the number of valence electrons of the elements in that column • The only exception is He which only has two valence electrons but is located at the far right due to similarities in chemical behavior to that group

10. What is the number of valence electrons for the following atoms? • Carbon (C) • Hydrogen (H) • Oxygen (O) • Nitrogen (N) • Boron (B) • Chlorine (Cl) • Potassium (K) • Strontium (Sr) • Astatine (At) • Neon (Ne) • Bromine (Br) • Sodium (Na)

11. Answers

12. What is the number of valence electrons for the following atoms? • Carbon (C) • Hydrogen (H) • Oxygen (O) • Nitrogen (N) • Boron (B) • Chlorine (Cl) • Potassium (K) • Strontium (Sr) • Astatine (At) • Neon (Ne) • Bromine (Br) • Sodium (Na) • 4 • 1 • 6 • 5 • 3 • 7 • 1 • 2 • 7 • 8 • 7 • 1

13. Ion • An atom in which the total number of electrons is not equal to the total number of protons • The atom has a net positive or negative electrical charge

14. Determining an Atom’s Charge • Atomic number - number of electrons actually present in the atom = overall electrical charge of atom • Atoms are “happiest” with full valence shells (8 electrons) • They will interact with other atoms and gain or lose electrons to achieve this

15. Determining an Atom’s Charge • Elements in groups 1 – 3 “find it easiest” to loose electrons and thus make positive ions or cations • Elements in 5 – 7 “find it easiest” to gain electrons and thus make negative ions or anions • The number of electrons gained or lost will determine the charge • i.e. loss of 1 electrons = +1 charge

16. Example • Using a periodic table determine what charge the following elements would likely have. • Na • As • Br • S • Mg • B

17. Answers • Na: +1 • As: -3 • Br: -2 • S: -1 • Mg: +2 • B: +3