Building Atoms!

AP Biology

On your paper

• Label Notes 2.1

Categories

• Cheerios – Electrons• Smarties – Protons• Starbursts - neutrons

Build a Helium Atom

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?

Build Hydrogen

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?

How many electrons fit each orbital?

• First – 2• Second -8• Third -8

Build Nitrogen

• Is nitrogen electrically stable?• What does nitrogen need to be electrically stable?

Build Oxygen

• Is oxygen electrically stable?• What does oxygen need to be electrically stable?• Is oxygen more reactive than nitrogen?

Build Fluorine.

• Is Fluorine electrically stable?• What does Fluorine need to be electrically stable?• Is fluorine more reactive than nitrogen? Oxygen?

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?

PDQ 2.1

1. Atom vs. Element

Atom• Basic unit of matter• Composed of protons,

neutrons and electrons

Element• 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

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

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

3. Continued. Label and define

Electron Cloud

Neutron

Proton

Electron Cloud – Darker areas show probable location of where electrons would be.

nucleus

Center of an atom where the protons and neutrons are located.

3. Continued. Label and Define

electron

proton

neutron

Orbital/Electron Shell

Paths where electrons travel have varying distances from nucleus

4. Atomic Mass vs. Atomic Number

Atomic Mass• 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

Atomic Number• Equal to the number of

protons• Unique to each element• Oxygen is number 8 and

therefore has 8 protons.

5. Atomic mass vs. Atomic Weight

Atomic Mass• Mass of a single atom or an

individual isotope

Atomic Weight• 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.

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.

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)

8. What determines interactions between atoms?

• Number of electrons

8. Continued… Valence electrons

• Valence electrons are the electrons that are on the outermost electron shell.

• They determine how reactive the atom will be.

8. Continued…One covalent bond.

Carbon – 4Nitrogen – 3Oxygen - 2

Phosphorus – 3Sulfur - 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…..