BIO 204

What is an atom?

The smallest unit of an element that still behaves and interacts like such element

What is a molecule?

two or more types of atoms bonded together

What are the parts of an atom? Draw and label.

What is the weight of

• a proton

• a neutron

• an electron

Proton - 1 atomic mass unit (amu)

Neutron - 1 atomic mass unit (amu)

Electron - nearly massless compared to the weight of the protons and neutrons

Label and explain each part of the picture

3 - atomic number (also number of protons)

Li - element symbol

6.941 - atomic mass number (the average mass of the element and its various isotopes)

What is an isotope?

A version of an element that has the same number of protons and electrons, but either less than or more than the standard number

Why is atomic mass not just a whole number (since mass is measured in AMU, and protons and neutrons make up the mass of an atom and weigh 1 AMU)?

It is the average mass of the element and its isotopes. It is calculated based off of how common each isotope is in nature, so it is multiplying the mass of each natural isotope by its fractional abundance.

What is a valence electron?

The electron(s) on the outermost shell of an atom.

How many electrons are held in each shell of an atom (in terms of biology, 3rd shell is not exact)?

1st shell - two electrons max

2nd shell - 8 electrons max

3rd shell (has 3 sub-shells) - the first two sub shells hold 2 and 6 (8 total) max

For neutral elements, how do you find the number of electrons?

The number of protons (atomic number)

What are two important characteristics about noble gasses when relating to their electrons and interactions?

• All electron shells are full

• They do not form bonds with other atoms

What are the two fundamental “desires” of an atom? How do they fill these desires?

• They want to fill their outer shell

• They want to be neutral

by bonding!

What happens to the electrons of atoms in a covalent bond?

the bonded atoms share their electrons to fill their shells

What happens to the electrons of atoms in an ionic bond?

the bonded atoms either give up their electrons or gain electrons from the other atom

What is the new valence electron shell for the atom that gave up their atom(s) during ionic bonding?

The closest, filled shell becomes the new valence shell.

For example, if an atom gave up the electrons on their third shell, the second shell becomes the new valence electron shell.

How can you use the periodic table of elements to find the number of valence electrons for an atom?

• For columns 1 and 2, the column number is equal to the number of valence electrons

• For columns 13-18, the column number minus 10 is equal to the number of valence electrons

• For other columns, this trick does not work and you must perform electron configuration

What are the three kinda of subatomic particles?

• protons

• neutrons

• electrons

What determines each element’s particular chemical behavior?

the number of its subatomic particles

Why are neutrons essential for atoms?

they allow multiple protons to exist in the nucleus and prevent them from repelling against each other because each proton sticks to the attractive neutron

How many protons and neutrons are in hydrogen? Why?

• only one proton, no neutrons

• since there is no other proton in the nucleus to repel hydrogen’s proton, no neutron is needed

Describe the movement of the different subatomic particles in the nucleus.

• proton - still, in the nucleus

• neutron - still, in the nucleus

• electron - moving rapidly around the nucleus

What is the group of the most stable and “happy” elements called? What makes them stable?

• Noble gasses

• All of their electron shells are filled, so they are balanced and have no cravings for electrons

Are the noble gasses important for living processes?

Not really

Chlorine has 7 electrons on its third shell, so how “hungry” for electrons is chlorine?

VERY hungry, the most

Lithium and sodium have 1 valence electron, so how hungry are they for electrons? What is the fastest path to getting them stable?

• Not hungry

• To stabilize, it is easier for them to lose one electron

Carbon has 4 valence electrons, so which is the best path for this element to stabilize? What does this make carbon good for?

• it can lose or gain 4 electrons just as easily, both are good

• it is an ideal element for carrying on chemical reactions

Based off of the annotated periodic table from the beginning of the semester, from memory, annotate a periodic table describing which side is hungry for electrons, ready to give up electrons, which are ambivalent, and which are stable.

Look to BIO 204 journal pg. 5

What is another element that is “electron neutral”, similar to carbon?

Hydrogen

• it just needs one electron, but also only has one electron

• so, gaining or losing an electron would make it stable

What is a covalent bond?

a bond between two or more atoms where electrons are shared to fill both of the electron shells and make the atoms more stable

When two oxygen atoms bond together, how many electrons are shared? What is this type of bond called?

• four electrons are shared

• double bond

Which elements does SPONCH stand for?

Sulfur

Phosphorus

Oxygen

Nitrogen

Carbon

Hydrogen

What is the preferred number of covalent bonds for each element in SPONCH?

Sulfur - 2

Phosphorus - 5

Oxygen - 2

Nitrogen - 3

Carbon - 4

Hydrogen - 1

Think of SPONCH 252(like my student id)341

252341

What type of force is a covalent bond? Describe its strength in relation to other bond types.

• Intramolecular force

• Very strong compared to other bond types

What happens to an atom when it gains an extra electron? What type of molecule is this called (it is now a molecule because gaining an electron is a result of bonding)?

• It becomes negatively charged

• It is now an ion

What happens to atoms like lithium when they lose their electron? What do we call this molecule now?

• it becomes positively charged

• it is also an ion now

What happens when a “hungry” atom and an atom that is more ready to give up an atom form a covalent bond? Why? What does this create?

• the sharing of electrons is uneven

• electrons spend longer around the more “hungry” atom

• it creates a partial charge

What do we call molecules with charge separation?

polar molecules

What does it mean that water is maximally polar? What unique ability does this give the molecule?

• it has the largest separation of charges

• it is the “universal solvent” and can dissolve more molecules than any other liquid

What do δ⁺ and δ− indicate? In a water molecule, which would be on the oxygen side and which would be on the helium side?

• partially positive and partially negative

• the δ− would be on the oxygen side

• the δ+ would be on the hydrogen side

Why is it particularly helpful that living cells are 70% water?

a very wide range of chemicals can be used and absorbed

What quality of water make it attracted to itself?

its polarity/partial charge (the δ+ side/H side is attracted to the δ− side/O side)

What are the weakest intermolecular interactions called? Describe the interaction?

• hydrogen bonds

• the partially positive part of a molecule/ion (hydrogen is usually the partially positive part) is attracted to the partially negative part of another molecule/ion

What are the five unusual properties of water?

1. Heat capacity - the hydrogen bonds between water molecules store heat energy

2. Hydrogen bonds between water are more separate in the solid form, so ice is less dense and thus floats

3. It takes a lot of heat energy to break the bonds between multiple water molecules, so evaporation makes the surrounding atmosphere cooler (think of dry heat vs. humid heat)

4. Cohesion - water molecules stay together strongly in the face of forces like gravity and wind

5. Polarity - water molecules are attracted to the opposite charges on other water molecules

What does it mean when a molecule is non-polar? Do atoms in a non-polar molecule have the same or different level of “craving” for electrons?

• it has no charge and no separation of charges

• they have equal affinity for electrons (eg. two hydrogen atoms or a carbon and a hydrogen atom

What combination of carbon and hydrogen have “electron hoarding” leading to a partial electric charge?

none!

Much of life consists of bonds between which two elements? Why is this?

• carbon and hydrogen

• all combinations are non-polar and have no separation of charges

What is a consequence of being non-polar? (Why grease doesn’t wash away with water)

water cannot dissolve it