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

2. Atoms are extremely small
Atoms are extremely small. One teaspoon of water has 3x as many atoms as the Atlantic Ocean has teaspoons of water!

3. The ATOM The atom is mostly empty ________
Most of the mass of an atom is in the _______.
Protons and neutrons have a mass of _____.
Atomic mass = _________________

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

5. ATOM COMPOSITION: CHARGES
Protons have a
charge of ____
Electrons have a charge of ______
Neutrons have _____ charge

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

7. Electrons
• the number of electrons is ______ to the number of protons since elements have no charge.

8. Electrons
• the number of electrons is equal to the number of protons since elements have no charge.
This means the atomic number tells us the # of protons and it tells us the number of electrons that are in an element.

9. •Atomic number: number of protons in an atom, =
•Atomic number: number of protons in an atom, = number of electrons in electron cloud
• Atomic mass: number of protons plus neutrons

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

11. atomic mass – atomic number
Nickel: protons neutrons
# neutrons =
atomic mass – atomic number

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

13. Atomic mass= 184
Atomic number = 74
74 protons, 74 electrons
110 neutrons (184 – 74 = 110)

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

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

16. 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)

17. Atomic Symbols for Isotopes: 2 Ways
name of the element and the mass number: sodium-23, sodium-24
mass number and atomic number in symbol form
mass number
23 Na atomic number

18. Which of the following represent isotopes of the same element?
Which element is it?
234 X X X X

19. 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)

20. Composition of molecules is given by a MOLECULAR FORMULA
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
H2O
C8H10N4O2 - caffeine

21. ELEMENTS THAT EXIST AS DIATOMIC MOLECULES
Remember:
The “GENS”
These elements exist as PAIRS when ALONE.
Hydrogen (H2)
Nitrogen (N2)
Oxygen (O2)
Halogens
(F2, Cl2, Br2, I2)
(P4 and S8)