Download 8th-interlude-for-atoms - Epiphany Catholic School

th
8
Grade
An interlude for atoms
Element
Contains only one type of atom
Organized in Periodic Table
* 90 occur in nature
* 114 in total. (Could this change?)
Iron
Gold
Beryllium
Phosphorus
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
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.
the Periodic Table
Atomic
Element Number
Oxygen
p+
e-
Mass
Number Neutrons
8
16
19
39
Potassium
Uranium
Aluminum
92
142
13
14
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.
Isotopes:
have the same number of protons but different number of neutrons.
How are isotopes used?
 To treat some types of cancer
 Geologists use them to date some rocks & fossils.
Problems:
1. A has 24 protons & 25 neutrons.
B has 24 protons & 26 neutrons.
Are A & B different elements or isotopes?
2. 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?
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
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)
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)
Examples?
7 is neutral
Living things rely on their pH remaining constant
Acid pH in body of water
Acid rain