2. * What is an atom? ~ An atom is the smallest particle of an element. element. ~ It is made of a nucleus surrounded by 1 or more electrons. more electrons. * Can an atom be separated into smaller parts? ~ Yes, it can be separated into: - protons - neutrons - electrons

3. Protons Found in the nucleus They are positively charged Attract to electrons Each proton has an atomic mass of 1 atomic mass unit (1 amu). +

4. Neutrons Found in the nucleus They are not charged – neutral Each neutron has an atomic mass of 1 amu.

5. Electrons Found outside the nucleus Negatively charged. Attract protons They have no mass (insignificant). -

6. The atomic number is the number of protons of an atom. Each element has a unique number of protons. The # of protons = the # of electrons (only in a neutral atom).

7. Atomic Mass Atomic mass = # of protons + # of neutrons for each atom. Measured in ‘ atomic mass unit ’ (amu)

8. Electrons move around the nucleus. They take a huge space compared to the nucleus volume. Some electrons are closer to the nucleus than others.

9. Role of Valence Electrons Outer most electrons. # of valence electrons range from 1 to 8. Each element has a typical valence #. - oxygen has 6 - carbon has 4 - hydrogen has 1

10. Role of valence electrons continues… Valence electrons can be represented by ‘electron dot diagram’. OHC In a chemical bond, the number of the valence electrons are given away, or they increase to 8.

11. Dmitri Mendeleev (1834-1907) - Russian Chemist - Developed first periodic table 1869 1869 - 63 known elements

12. Left gaps for undiscovered elements Found the atomic mass to be the key to the arrangement Atomic number was discovered later in the early 1900s.

13. In each square you find: ~ atomic number on the top = proton # ~ proton # = electron # ~ element symbol below a. n. ~ element name ~ atomic mass (decimal #s) ~ atomic mass = proton mass + neutron mass mass * An element ’ s properties can be predicted from its location in the table. 6 C Carbon 12.011

14. Elements in the same column have similar chemical and physical properties. There are 18 columns called groups or families. 7 rows of elements called periods. Their reactivity decreases from left to right.

15. Because it is based on the structure of atoms, especially the valence electrons. Group 1 Group 2 Group 13 Group 14 Group 1 Group 2 Group 13 Group 14 Li Be B C Lithium Beryllium Boron Carbon Lithium Beryllium Boron Carbon Valence e- 1 2 3 4

16. Many periodical elements are required for your well being and survival. They are called essential elements. Deficiency or lack of any of the essential elements can result in illness or death.

17. 12 of the about 30 essential elements are: - OxygenO - CarbonC - HydrogenH - NitrogenN - CalciumCa - PhosphorusP

18. - SodiumNa - PotassiumK - ChlorineCl - SulfurS - MagnesiumMg - IronFe