1. 8th Grade
An interlude for atoms

2. Contains only one type of atom Organized in Periodic Table
Element
Contains only one type of atom
Organized in Periodic Table
* 90 occur in nature
* 114 in total. (Could this change?)
Sure it could – as scientists discover more elements

3. Iron
Gold
Beryllium
Phosphorus

4. Meet the Elements video - https://www.youtube.com/watch?v=Uy0m7jnyv6U

5. Atom – smallest unit of element that has properties of that element
* Nucleus – made of protons (positive charge) & neutrons (no charge).
- Has 99% of mass but only 1/100,000 of size.
* Electron cloud – negative charge. Electrons can be anywhere in cloud
Parts of an atom video -

6. Atomic Number = number of protons (also number of electrons).
Why does the nucleus have a positive charge?
Has protons which are positively charged.
Atoms are neutral. Why?
Protons are equal to electrons.
Atomic Number = number of protons
(also number of electrons).
Mass Number = equal to the sum of protons & neutrons in nucleus.

7. the Periodic Table
Page R12 and R13 in Dynamic Earth Book

9. p+ e- 8 16 19 39 92 142 13 14 Element Atomic Number Mass Oxygen
Neutrons
Oxygen 8 16
Potassium 19 39
Uranium 92
142
Aluminum 13 14

10. If the number of protons in 2 atoms is different then you have different elements.
ex. 4 protons 5 protons
beryllium boron
If you have same number of protons in two substances but different neutrons, then you have the same elements but they are called isotopes.

11. Isotopes:
have the same number of protons but different number of neutrons.

12. A has 24 protons & 25 neutrons. B has 24 protons & 26 neutrons.
How are isotopes used?
To treat some types of cancer
Geologists use them to date some rocks & fossils.
Problems:
A has 24 protons & 25 neutrons.
B has 24 protons & 26 neutrons.
Are A & B different elements or isotopes?
C has an atomic number of 12 & mass number of 24.
D has an atomic number of 13 & a mass number of 26.
Are C & D different elements or isotopes?
Same element (Chromium) but isotopes
Different elements (12 is Magnesium 13 is Aluminum)

13. Compounds Formed when atoms of more than one element combined.
Properties of a compound are very different from properties of the elements that make it up.
Ex. NaCl = salt
Natural State
Color
Problems
Na (sodium)
Solid metal
Silvery
Explosive in water
Cl (chlorine)
Gas
Greenish
poisonous
NaCl (salt)
Solid crystal
White OK

14. Atoms can gain or lose electrons This makes them ions
Why is the overall charge of an uncharged atom zero?
It has the same number of protons as electrons
If a Hydrogen atom lost an electron, would it be positive or negative?
Positive – there would be more protons than electrons
H+ (hydrogen ion)

15. pH pH measures how acidic and basic something is
Acids are 0-6 – have H+ ions (hydrogen ions)
Examples?
Bases are 8-14 – have OH- (hydroxide ions)
7 is neutral

17. Living things rely on their pH remaining constant
Acid pH in body of water
Acid rain