AP BIO CHAPTER 2

Matter

Matter is anything that takes up space and has mass

Element

A substance that cannot be broken down to other substances by chemical reactions

Compound

A substance consisting of two or more elements in a fixed ratio, with properties different from its elements

Essential elements

About 20–25% of the 92 natural elements are required for life

CHON

Carbon, Hydrogen, Oxygen, Nitrogen make up 96% of living matter

Other major elements

Calcium, Phosphorus, Potassium, Sulfur make up most of the remaining 4% of living matter

Trace elements

Elements required in only minute quantities

Adaptation to toxic elements

Some species evolve adaptations to survive in environments with toxic elements (e.g., plants on serpentine soil)

Atom

The smallest unit of matter that retains the properties of an element

Proton

Subatomic particle with a positive charge

Neutron

Subatomic particle with no electrical charge

Electron

Subatomic particle with a negative charge

Atomic nucleus

Center of the atom containing protons and neutrons

Electron cloud

Region around the nucleus where electrons are found

Dalton

Unit used to measure atomic mass

Atomic number

Number of protons in the nucleus

Mass number

Sum of protons and neutrons in the nucleus

Atomic mass

Approximate total mass of an atom, close to mass number

Isotope

Atoms of the same element with different numbers of neutrons

Radioactive isotope

Isotopes that decay spontaneously, releasing particles and energy

Radioactive tracer

Used to track atoms through metabolism or in medical imaging (e.g., PET scans)

Radiometric dating

Measuring isotope ratios and half-lives to determine the age of fossils/rocks

Half-life

Time it takes for half of a radioactive isotope to decay

Carbon-14

Special isotope used for dating and part of CHON

Energy

Capacity to cause change

Potential energy

Energy matter has because of location or structure

Electron shells

Regions around the nucleus with specific energy levels

Chemical behavior

Determined by the distribution of electrons in shells

Noble gases

Already stable

do not need more valence electrons

Electronegativity

An atom’s desire for electrons

Covalent bond

Sharing of valence electrons between atoms

Single bond

Sharing of one pair of electrons

Double bond

Sharing of two pairs of electrons

Ionic bond

Complete transfer of electrons between atoms with large electronegativity differences (e.g., NaCl)

Nonpolar covalent bond

Equal sharing of electrons (electronegativity difference < 0.5)

Polar covalent bond

Unequal sharing of electrons (difference > 0.5 but < 1.7)

Water polarity

Water is polar because oxygen is more electronegative, making O partially negative and H partially positive

pH

Measurement of hydrogen ion concentration in a solution

Acid

More H⁺ ions, lower pH

Base

Fewer H⁺ ions, higher pH

Neutral pH

7 on the pH scale

Molecular shape

Determines function and how molecules interact

Orbital hybridization

Positions of orbitals in covalent bonds determine molecular shape

Opiates vs endorphins

Similar shapes bind the same brain receptors, causing similar effects

Chemical reaction

Making and breaking of chemical bonds

Reactants

Starting molecules of a reaction

Products

Resulting molecules of a reaction

Photosynthesis

Conversion of CO₂ and H₂O into glucose and O₂ powered by sunlight

Reversible reaction

Reaction that can go forward and backward

Chemical equilibrium

Forward and reverse reaction rates are equal, concentrations stay constant