1. An atom consists of a Nucleus () Nucleus (protons and neutrons) Electrons. Electrons in space about the nucleus. The Atom Nucleus Electron cloud

2. The ATOM Most of the mass of an atom is in the nucleus. Protons and neutrons have a mass of 1. Atomic mass = # protons + # neutrons The atom is mostly empty space

3. Electrons the number of electrons is equal to the number of protons since elements have no charge. Electrons are extremely small. One teaspoon of water has 3 times as many atoms as the Atlantic Ocean has teaspoons of water. Travel around the nucleus in the electron cloud which is mostly empty space

4. ATOM COMPOSITION: CHARGES Neutrons have NO charge Protons have a charge of + 1 Electrons have a charge of - 1

5. A tomic number: number of protons in an atom, = number of electrons in electron cloud Atomic mass: number of protons plus neutrons Most common ions

6. An element has 28 protons and 31 neutrons: What is it?

7. Nickel: 28 protons, 31 neutrons # neutrons = atomic mass – atomic number

8. An element has an atomic mass of 184. How many protons does it have? How many electrons does it have? How many neutrons does it have?

9. Tungsten: Atomic mass = 184 Atomic number = 74 74 protons, 74 electrons 110 neutrons (184 – 74 = 110)

10. Isotopes Atoms of the same element but different mass number. Boron-10 ( 10 B) has 5 p and 5 n Boron-11 ( 11 B) has 5 p and 6 n 10 B 11 B

11. Isotopes & Their Uses Bone scans with radioactive technetium-99.

12. CARBON-14 – RADIOACTIVE ISOTOPE Occurs in trace amounts in the atmosphere Absorbed into living organisms The half-life of carbon- 14 is approx 5700 years (when half the C-14 is converted to N-14)

13. Atomic Symbols for Isotopes: 2 Ways Show the name of the element, a hyphen, and the mass number: sodium-23, sodium-24 or show the mass number and atomic number in symbol form mass number 23 Na atomic number 11

14. Isotopes? Which of the following represent isotopes of the same element? Which element is it? 234 X 234 X 235 X 238 X 92 93 92 92 1 2 3 4

15. Compounds a pure substance composed of 2 or more elements in a fixed ratio that can be separated by heat and electricity properties differ from those of individual elements Ex : table salt (NaCl)

16. A MOLECULE is 2 or more NONMETAL atoms bonded together by COVALENT BONDS– they may be the same element (ie diatomic molecule) or they may be different elements (ie caffeine) Composition of molecules is given by a MOLECULAR FORMULA H2OH2OH2OH2O C 8 H 10 N 4 O 2 - caffeine

17. ELEMENTS THAT EXIST AS DIATOMIC MOLECULES Remember: The “GENS” These elements exist as PAIRS when ALONE. Hydrogen (H 2 ) Nitrogen (N 2 ) Oxygen (O 2 ) Halogens (F 2, Cl 2, Br 2, I 2 ) (P 4 and S 8 )