Bio chapter 2

What is matter?

Anything that has mass and occupies space.

What is an element?

A pure substance that cannot be broken down further by ordinary chemical means.

What is an atom?

The smallest unit of an element that retains its properties.

What is a molecule?

Two or more atoms bonded together.

What is a compound?

A molecule with atoms from different elements (e.g., H2O, CO2).

What 4 elements make up 96.5% of living organisms?

Carbon, Hydrogen, Oxygen, Nitrogen.

What 7 elements make up most of the other 3.5% of life?

Calcium, Phosphorus, Potassium, Sulfur, Sodium, Chlorine, Magnesium.

What are trace elements?

Elements needed in very small amounts but are essential (e.g., iodine).

What particles are in the atomic nucleus?

Protons (+) and Neutrons (neutral).

What is the atomic number?

The number of protons in the nucleus, which identifies the element.

What is the mass number?

The total number of protons and neutrons in the nucleus.

What is a dalton (Da)?

A unit of atomic mass = the mass of one proton or neutron.

What is an isotope?

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

What is a radioisotope?

An unstable isotope that decays and releases radiation.

What is the difference between mass and weight?

Mass is the amount of matter; weight is mass under gravity.

What is an orbital?

A region in space where an electron is most likely to be found.

What is an electron shell?

Energy levels containing groups of orbitals at similar distances from the nucleus.

What are valence electrons?

Electrons in the outermost shell; they determine reactivity.

What is an ionic bond?

Bond formed by transfer of electrons between atoms (cation + anion).

What is a covalent bond?

Bond formed when atoms share electrons.

What is a polar covalent bond?

Unequal sharing of electrons causing partial charges (δ+ and δ-).

What is a nonpolar covalent bond?

Equal sharing of electrons with no partial charges.

What is a hydrogen bond?

Weak attraction between a δ+ hydrogen and a Î- atom in another bond.

What are van der Waals forces?

Weak, temporary attractions due to shifting electron distributions.

What is a chemical reaction?

Process of breaking and forming bonds between atoms/molecules.

Why is water less dense as ice?

Hydrogen bonds form a rigid lattice that spaces molecules farther apart.

What is cohesion?

Water molecules sticking to each other via hydrogen bonds.

What is adhesion?

Water molecules sticking to other surfaces.

What is surface tension?

Resistance of water surface to breaking due to hydrogen bonding.

Why does water have high specific heat?

It absorbs/release heat without large temperature changes due to hydrogen bonds.

What is heat of vaporization?

Amount of heat required for water molecules to escape as gas.

Why is water called the universal solvent?

Its polarity allows it to dissolve polar and ionic substances.

What is an acid?

A substance that donates H+ ions (proton donor).

What is a base?

A substance that accepts H+ ions or releases OH- (proton acceptor).

What is the pH scale?

A 0-14 scale measuring acidity or alkalinity based on H+ concentration.

What is a buffer?

A substance that stabilizes pH by absorbing or releasing H+ ions.

What is the main buffer in human blood?

The carbonic acid-bicarbonate system.