Pre Chemistry Review

Subatomic particle layout

Protons and neutrons live in the nucleus; electrons orbit in 3D regions outside.

Proton charge and mass

Positive charge (+1) with a mass of 1 atomic mass unit (amu).

Neutron charge and mass

Neutral/no charge (0) with a mass of 1 atomic mass unit (amu).

Electron charge and mass

Negative charge (-1) with a negligible mass not counted in the mass number.

Neutral atom rule

 Holds an exactly equal number of protons and electrons to balance the net charge to zero.

Element

A pure substance that cannot be broken down chemically; defined by its specific number of protons.

Matter

Anything that has mass and takes up physical space (solids, liquids, and gases).

Isotopes

Atoms of the same element with the same number of protons but a different number of neutrons.

Atomic Number

 The number of protons in an atom; located at the top of the periodic table card.

Mass Number

 The sum of protons and neutrons in a specific atom; a whole number NOT found on the periodic table.

Atomic Mass

The decimal average weight of all natural isotopes; located at the bottom of the periodic table card.

Molecules

Two or more atoms held together firmly by covalent chemical bonds.

Trace Elements

Essential elements required by an organism in microscopic quantities to survive (like Iodine or Iron).

Orbital

A 3D region of space around the nucleus where there is a ninety percent probability of finding an electron.

Electron Shells

Discrete energy levels where electrons reside; energy increases further from the nucleus.

Octet Rule

The tendency of atoms to prefer a completely full outer shell of 8 electrons to become energetically stable.

Inert Atom

 An atom with a completely full valence shell that is stable and chemically unreactive.

Valence Electrons

 The electrons located in the outermost shell that directly dictate chemical reactivity and bonding.

the four elements making up 96 percent of living matter.

CHON Elements — Carbon, Hydrogen, Oxygen, and Nitrogen

the building blocks of biological macromolecules

SPONCH Elements — Sulfur, Phosphorus, Oxygen, Nitrogen, Carbon, Hydrogen

Chemical Bond

 An attraction between atoms that occurs as they share, lose, or gain valence electrons to reach stability.

Covalent Bond

 A strong chemical bond formed when two atoms share a pair of valence electrons.

Double Covalent Bond

 A covalent bond where two atoms share four electrons total (two pairs) directly with each other.

Breaking chemical bonds

A process that always requires an input of energy to pull atoms apart.

Forming chemical bonds

A process that always releases energy as atoms drop into a lower, stable energy state.

Electronegativity

 An atom's chemical property describing its relative strength to attract and pull shared electrons.

Polar Covalent Bond

 Formed when atoms have different electronegativities, causing an unequal sharing of electrons and partial charges.

Nonpolar Covalent Bond

Formed when atoms have equal or highly similar electronegativities, sharing electrons perfectly equally.

Carbon-Hydrogen Bond (C-H)

A completely nonpolar bond because both elements share almost identical electronegativity values.

Hydrophobic Barrier

 Formed by nonpolar lipid tails (hydrocarbons) which lack charges and naturally repel water.

Phosphate Group (PO4)

A highly polar, negatively charged functional group because weak Phosphorus is surrounded by greedy Oxygen hogs.

Hydrophobic Interactions

An interaction where nonpolar molecules clump together to minimize contact with polar water molecules.

Ionic Bond

 A strong chemical bond formed by the electrostatic attraction between a positive cation and a negative anion.

Cation

A positively charged ion formed when an atom loses one or more valence electrons.

Anion

A negatively charged ion formed when an atom gains one or more valence electrons.

Hydrogen Bond

A weak attraction between a partial positive Hydrogen in one molecule and a partial negative Oxygen or Nitrogen in another.

Van der Waals Interactions

 Extremely weak, fleeting attractions between nonpolar molecules caused by random, temporary electron imbalances.

Why water is polar

Oxygen is highly electronegative and pulls shared electrons away from Hydrogen, creating partial charges.

Density of Ice

Water is less dense as a solid because hydrogen bonds expand into a rigid crystal lattice, causing ice to float.

Density of Ice

Water is less dense as a solid because hydrogen bonds expand into a rigid crystal lattice, causing ice to float.

High Specific Heat of Water

Water resists temperature changes because a massive amount of energy is required to break its hydrogen bonds first.

Cohesion vs Adhesion

 Cohesion is water sticking to water (surface tension); Adhesion is water sticking to other surfaces

Hydration Shell

 A caging sphere of water molecules that crowds around and dissolves a separated ion based on matching opposite charges.

The pH Scale

A scale running from 0 to 14 that measures the concentration of free Hydrogen ions on a negative log scale.

Acidic Solution

A solution with a pH from 0 to 6.9 containing a high concentration of Hydrogen ions.

Basic Solution

 A solution with a pH from 7.1 to 14 containing a low concentration of Hydrogen ions.

Chemical Buffer

A weak acid or base system (like blood bicarbonate) that prevents drastic pH shifts by absorbing or releasing Hydrogen ions.