AP Biology Chapter 2

• Matter is anything that has mass/ takes up space.
• Atoms are the smallest unit of an element that has the properties of that element.
• Matter is composed of subatomic particles : Protons, Neutrons, and Electrons.
• Electrons= negatively charged and orbit around the nucleus.
• element= a substance that can’t be separated or broken down into simpler substances by chemical means.
• Of the 118 elements, 92 occur naturally
• hydrogen (h), carbon (c), nitrogen (n), oxygen (o), phosphorus (p), and sulfur (s) make up 98% of the mass of living organisms.
• Columns on the Periodic Table are based on number of valence electrons.
• Valence electrons are electrons located on the outer shell.
• Atomic mass is the number of neutrons/ protons in an atom.
• Isotopes= atoms that have the same number of protons/ electrons but different number of neutrons.
• Octet Rule= atoms, in an attempt to become stable, fill their outermost energy level.
• Most atoms require 8 electrons in the outer shell (2 electrons in the first shell), while hydrogen/ helium only need 2 electrons in the outer level.
• When the outer shell is filled, an atom is stable.
• Some atoms are naturally stable, meaning they are inert.
• To fill their outer shells, atoms form bonds.
• Molecule= 2 or more atoms linked by chemical bonds.
• Compound= a molecule composed of different kinds of atoms.
• Bond= energy forces joining 2 or more atoms.
• Covalent bonds= a chemical bond that arises from the sharing of electrons between 2 atoms
• Non-polar bonds= bond between 2 atoms in which the electric charge is evenly balenced
• Polar bonds= bond between 2 atoms in which electrical charge is not evenly shared
• Ionic bonds= an electrostatic attraction between a positively and a negatively charged ion (charged particle or atom) (one atom transfers an electron(s) to another atom)
• Cations are atoms which lose electrons/ become positive.
• Anions are atoms which gain electrons/ become negative.
• Hydrogen bond= weak electrostatic bond that arises from the attraction between the slightly positive charge on one hydrogen atom and the slightly negative charge on a nearby atom (usually oxygen).
• Models include Bohr Model, Structural Formula, Ball and stick model, Space filling model.
• Maximum Number of Covalent Bonds: Hydrogen: 1, Oxygen: 2, Sulfur: 2, Nitrogen: 3, Carbon: 4, Phosphorus: 5.
• Water(H20) is 70% of humans and is necessary for all living organisms, it has a unique structure with special properties.
• protons= positively charged and located in the nucleus of an atom
• neutrons= neutral and located in the nucleus of an atom
• periodic table= table that groups all known elements according to their physical and chemical properties
• An atom's mass is relative to hydrogens
• Solid water is less dense than liquid water (ice floats)
• specific heat= amount of heat required to change 1g of substance by 1 degree C
• Water has a high specific heat (it takes longer to heat up and cool down)
• Cohesion= an attraction between substances of the same kind (e.g. the surface of water is stiff)
• adhesion= an attraction between different substances that causes them to stick together (explains why some substances get wet)
• Cohesion and adhesion are responsible for capillary action
• Capillary action= process in which water molecules are pulled through something because water reacts with the material and pulls other water molecules with it