BIO101 Unit 1 Chapter 2

What are the three subatomic particles and their charges?

Protons (+), neutrons (0), electrons (–)

Where are protons and neutrons located?

In the nucleus

Where are electrons found?

In orbitals within electron shells around the nucleus

What determines the potential energy of electrons?

Their distance from the nucleus — farther = higher energy.

What is the valence shell?

The outermost electron shell containing valence electrons.

Why are valence electrons important?

They determine chemical reactivity and bonding behavior.

What does atomic number indicate?

The number of protons in an atom.

What does atomic mass represent?

The average mass of all isotopes; roughly protons + neutrons.

How do you calculate neutrons?

Neutrons = mass number – atomic number.

What is electronegativity?

An atom’s attraction for shared electrons.

What type of bond forms between atoms with similar electronegativity?

Nonpolar covalent bond.

What type of bond forms between atoms with different electronegativity?

Polar covalent bond.

What happens in an ionic bond?

Electrons transfer completely from one atom to another, forming ions.

What is a cation?

A positively charged ion that has lost electrons.

What is an anion?

A negatively charged ion that has gained electrons.

What is a hydrogen bond?

A weak attraction between a partially positive hydrogen atom and an electronegative atom.

Why are hydrogen bonds important?

They give water many of its unique properties and stabilize biological molecules.

What are Van der Waals interactions?

Weak attractions caused by temporary charge shifts in atoms.

What is a chemical reaction?

A process involving breaking and forming of bonds to convert reactants to products.

What are reactants and products?

Reactants are starting substances; products are substances formed by the reaction.

What is the order of electron shell filling?

1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p …

How many electrons fit in the 1st electron shell?

2

How many electrons fit in the 2nd electron shell?

8

How many electrons fit in the 3rd electron shell filling?

18

What rule describes stability in outer shells?

The octet rule — atoms are most stable with 8 valence electrons (except for the 1st shell).