1. The Atom

2. The Atom
Definition: The smallest particle of an element that retains the properties of that element.
Democritus= the first person to suggest the existence of atoms

3. Dalton’s theory 4 parts:
1) All elements are composed of tiny indivisible particles called atoms
2) Atoms of the same element are identical.
The atoms of any one element are different from those of any other element.
3) Atoms of different elements can physically mix together or can chemically combine with one another to make compounds.
4) Chemical reactions occur when atoms are separated, joined, or rearranged.
Atoms never change into another element.

4. How big is an atom?
According to this picture: what is the atom mostly made up of?

5. Parts of the atom: Proton= Positively charged subatomic particle
Electron=Negatively charged subatomic particle
Neutron= Neutrally charged subatomic particle
Nucleus:
Protons & Neutrons
Electrons

6. Properties of Subatomic particles
Size of Particles
Properties of Subatomic particles
Particle
Symbol
Relative Electric Charge
Relative mass (g)
Actual Mass (g)
Electron E- 1-
9.11 x 10-28
Proton P+ 1+ 1
1.67 x 10-24
Neutron N°

7. Vocabulary
Atomic mass unit= 1/12 the mass of a carbon atom (what each atoms mass is measured in)
Atomic #= number of protons that an atom of an element contains
How many protons does carbon have?
How many protons does chlorine have?
How many protons does magnesium have?
Atomic mass= Weighted average mass of the atoms in a naturally occurring sample of an element.
Atomic mass = Protons + Neutrons

8. So, how do we count how many we have?
What is: Atomic #= Atomic mass=? # of Protons=? # of electrons=? # of Neutrons=? Symbol=? 6 C
12.011
# of P = # of e- in a neutral atom!

9. Carbon-12 Shorthand What is: Element =? Atomic #= ? Atomic mass=?
# of Protons=?
# of electrons=?
# of Neutrons=?
Symbol=?
Carbon-12

10. Shorthand What is: Element =? Atomic #= ? Atomic mass=? # of Protons=?
# of electrons=?
# of Neutrons=?
Symbol=?

11. Isotopes
Look at this picture….Based on your observations, what is an isotope?
If I change the # of protons to 7 is that a carbon isotope? Why or why not?

12. Isotopes Neon-20 Neon-21 Neon-22
Definition: Atoms that have the same # of protons but a different # of neutrons.
So, would the mass change?
What makes these isotopes?
What is different about them?
What is the # of Neutrons, protons, electrons, atomic mass, symbol, and element of each of these?
Neon-20
Neon-21
Neon-22

13. Isotope Practice!
1) Two isotopes of carbon are carbon-12, and carbon Write the symbol for each isotope using superscripts and subscripts to represent the atomic mass and the atomic number.
2) How many:
Protons?
Neutrons?
Electrons?

14. Atomic mass **Different than mass #
Find Carbon on your periodic table, what is the mass?
Do we only have one type of carbon?
We must find a relative atomic mass to represent all elements with isotopes. To do that we measure in AMU’s (atomic mass units)
We do this because each particle has such a tiny mass.

15. Atomic Mass
Atomic mass: Weighted average mass of the atoms in a naturally occurring sample of an element
AMU: atomic mass unit, 1/12 the mass of carbon-12 atom.
How do we find the atomic mass?
(Relative abundance of isotope # 1 X atomic mass of isotope 1) + (Relative abundance of isotope #2 X atomic mass of isotope # 2)

16. Atomic mass calculation reminders
**Always take it out of a percent!
**Always use the atomic mass for mass and not the rounded mass!
Let’s practice!

17. Ions Definition: atoms that have lost or gained electrons Examples:
Gain electrons + charged ion
Lose electrons - charged ion
The number next to the charge indicates how many electrons where lost or gained
Examples:
Sodium (Na)
Neutral atom: Na
Sodium Ion: Na+
Chlorine (O)
Neutral atom: O
Chloride Ion: O-2