1. Building Atoms!
AP Biology

2. On your paper
Label Notes 2.1

3. Categories smarties – Electrons Old candy – Protons
Green beads - neutrons

4. Draw & Label in notebook
Build a Helium Atom
# protons = atomic number
# neutrons = atomic mass rounded – protons
# electrons = # protons in stable atoms
Draw & Label in notebook

5. Suppose…. What is it called now?
The number of protons change?
The number of electrons change?
The number of neutrons change?
What is a radioisotope?
New element!
Ion
Isotope
Radioactive; unstable nucleus

6. Draw & Label in notebook
Build Hydrogen
Draw & Label in notebook

7. Predict in your notebook…
If Hydrogen gained a proton, what would it be called….
If hydrogen lost an electron, what would it be called…
If hydrogen gained a neutron?
Helium
Hydrogen ion
“oxidized”
Isotope
deuterium

8. How many electrons fit each orbital?
First – 2
Second -8
Third -8

9. Build Nitrogen Is nitrogen electrically stable?
What does nitrogen need to be electrically stable?
How many valence electrons does it have?

10. Build Oxygen Is oxygen electrically stable?
What does oxygen need to be electrically stable?
How many valence electrons does it have?
Is oxygen more reactive than nitrogen?

11. Build Fluorine. Is Fluorine electrically stable?
How many valence electrons does it have?
Is Fluorine electrically stable?
What does Fluorine need to be electrically stable?
Is fluorine more reactive than nitrogen? Oxygen?

12. What is electronegativity?
Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons
What is the trend of electronegativity on the periodic table?
Electronegativity increases from left to right and decreases from top to bottom down a column
Which elements are the most stable?
Which elements are the most reactive?

13. PDQ 2.1

14. 1. Atom vs. Element Atom Element Basic unit of matter
Composed of protons, neutrons and electrons
Pure substance
Contains only 1 kind of atom
Has unique characteristics that distinguish it from other elements
94 elements in nature
More than 24 have been made in laboratories

15. 2. 6 elements common in bio SPONCH Sulfur – found in certain proteins
Phosphorus – found in DNA
Oxygen – required for aerobic organisms
Nitrogen – found in DNA and protein
Carbon – basic atom in all organic molecules
Hydrogen – also in all organic molecules

16. 3. Describe atom structure
Composed of
Protons – in nucleus, positive charge
Neutrons – in nucleus, no charge
Electrons – in orbitals/electron cloud, negative charge
Most atoms are electrically neutral, which means the number of electrons = number of protons

17. 3. Continued. Label and define
Electron Cloud
nucleus
Neutron
Center of an atom where the protons and neutrons are located.
Proton
Electron Cloud – Darker areas show probable location of where electrons would be.

18. 3. Continued. Label and Define
electron
proton
neutron
Orbital/
Electron Shell
Paths where electrons travel  have varying distances from nucleus

19. 4. Atomic Mass vs. Atomic Number
Protons + Neutrons
Example – Oxygen has an atomic mass of 16. Because it has 8 protons and 8 neutrons.
The mass written on periodic tables refers to the average atomic mass. You would round this number to determine number of neutrons
Equal to the number of protons
Unique to each element
Oxygen is number 8 and therefore has 8 protons.

20. 5. Atomic mass vs. Atomic Weight
Mass of a single atom or an individual isotope
Is the average mass of all naturally occuring isotopes of an element
Also called average atomic mass.
This is what is on the periodic table.

21. 6. How to calculate number of neutrons
Number of neutrons = atomic mass (rounded) – number of protons
For example, nitrogen.
Protons = 7
Atomic mass is 14.
Number of neutrons = 14-7 = 7.

22. 7. Isotopes Have a different number of neutrons than it’s element
Each isotope has a different mass number.
Radioactive isotopes are radioactive and have an unstable nucleus. (They have excess nuclear energy)

23. 8. What determines interactions between atoms?
Number of electrons

24. 8. Continued… Valence electrons
Valence electrons are the electrons that are on the outermost electron shell.
They determine how reactive the atom will be.

25. 8. Continued… One covalent bond. Carbon – 4 Nitrogen – 3 Oxygen - 2
Phosphorus – 3
Sulfur - 2
All atoms thrive to have 8 electrons in their outer shell – octet rule. They will react to get it! Some want it more than others…..

26. Homework
Finish Reading Guide 2.2