1. Intro to parts of the atom
Unit 1 notes 2
Intro to parts of the atom

2. Synopsis of Structure
The atom is the smallest part of an element that retains its properties.
It is made of mostly empty space,with the majority of the mass concentrated in the middle (the nucleus).
The nucleus contains the positively charged protons and the chargeless neutrons.
The electrons are situated outside of the nucleus in the empty space in
energy levels (more on this later).

3. Warning: Oversimplification Ahead

4. Atomic number, mass number, atomic mass & isotopes

5. Atomic Number
The atomic number of an element tells you the number of protons in the nucleus.
Atoms are electrically neutral when found in elemental form, so the number of protons will be the same as the number of electrons.
Each element has a different atomic number.
Atomic number

6. Answer the following What element has atomic number 32?
How many protons does helium have?
What element has 79 protons?
What is uranium’s atomic number?
How many electrons does a neutral atom of calcium have?

7. Mass number
Most of the mass of an atom is in the nucleus; so much that the electrons can be neglected.
The mass number is the number of protons and neutrons in the nucleus.
If you know the mass number and the atomic number, you can determine the composition of an atom.
# of neutrons = mass number – atomic number

8. C 12 6 Carbon-12 Mass number, cont’d.
Composition can be written in shorthand by putting the symbol for the element with the mass number and atomic number to the left. C 12 6
Or, the mass number and chemical element can designate atoms, such as in:
Carbon-12

9. Answer the following How many neutrons are in potassium-39?
How many protons are in lead-208?
If an element has 22 protons and 26 neutrons, what is its mass number?
What element is in the previous question?
How many neutrons are in ? Hg

10. Isotopes
Atoms of the same element always have the same number of protons, but can have different numbers of neutrons.
An atom with the same number of protons but different number of neutrons are called isotopes.
Isotopes are chemically alike, because it is the protons which are responsible for the chemical behavior.

11. Answer the following
What is the difference between iodine-127 and iodine-125?
Is an element with 25 protons and 30 neutrons an isotope of one with 26 protons and 30 neutrons? Why or why not?

12. Elements in Compounds
When atoms chemically combine to make compounds, many times they lose or gain electrons.
Unequal numbers of protons and electrons means that the particle is charged.
Instead of calling these atoms, we call these ions.

13. Elements in Compounds Non- metals Metals
Metals tend to lose electrons in compounds, making them positive.
Nonmetals tend to gain electrons in compounds, making them negative

14. Answer the following How many electrons are in Ca2+?
How many electrons are in O2-?
How many protons are in P3-?

15. Atomic mass
Because there can be several isotopes of an element, there is another number, the atomic mass, that is the weighted average mass of all an element’s isotopes.
Carbon-12 was used as a reference to measure mass of atoms, and the carbon-12 atom was said to have a mass of exactly amu’s.
Atomic mass

16. Finding Weighted Avg.
Take into account both the mass of all isotopes as well as their relative abundances. For example:
There are two known stable isotopes of carbon; carbon-12 and carbon-13. If 99.0% is carbon-12 and the rest is carbon-13, what is the average atomic mass of carbon?

17. Finding Weighted Avg.
Zinc has five naturally occurring isotopes; zinc-64 (48.89%), zinc-66 (27.81%), zinc-68 (18.57%), zinc-67 (4.11%) and zinc-70 (0.62%). Based on this, what is the average atomic mass of zinc?

18. Elements and the Periodic Table

19. Arrangement of the table
The periodic table is arranged in order of increasing atomic number.
They are in groups according to similar chemical and physical properties.
What gives them similar properties?

20. Arrangement of the table
Elements in the same group have the same number of valence electrons.
This means they tend to lose or gain electrons in bonding the same way and make similar compounds.