LIFESCI 7A Lecture Notes - Lecture 1: Atomic Nucleus, Ionic Bonding, Hydrogen Bond
WEEK 1
2.1: Atoms and their properties
○ Elements: A pure substance, such as oxygen, copper, gold, or sodium, that cannot be further
broken down by the methods of chemistry.
○ Atom: the basic unit of matter
● Atoms consist of protons, neutrons, and electrons.
○ nucleus (of an atom): The dense central part of an atom containing protons and neutrons.
○ proton: A positively charged particle in the atomic nucleus.
○ electron: A negatively charged particle that moves around the atomic nucleus.
○ atomic mass: The mass of the atom determined by the number of protons and neutrons.
○ isotopes: Atoms of the same element that have different numbers of neutrons.
○ ion: An electrically charged atom or molecule (+ or -).
● Electrons occupy regions of space called orbitals
○ orbital: A region in space where an electron is present most of the time.
○ shell: An energy level in which an orbital can exist.
■ Note; Rutherford’s gold foil experiment: atoms are made up of mostly empty space and a
small, densely packed nucleus
● Elements have recurring, or periodic, chemical properties
○ periodic table of the elements: The arrangement of the chemical elements in tabular form,
organized by their chemical properties.
2.2: Molecules and Chemical Bonds
○ molecule: A substance made up of two or more atoms.
○ chemical bond: Any form of attraction between atoms that holds them together.
● A covalent bond results when two atoms share electrons
○ valence electrons: The electrons farthest from the nucleus, which are at the highest energy
level; combine with other valence electrons to form molecule
○ molecular orbital: A merged orbital traversed by a pair of shared electrons.
○ covalent bond: A chemical bond formed by a shared pair of electrons holding two different
atoms together.
○ double bond: A covalent bond in which covalently joined atoms share two pairs of electrons.
■ Note: bonding follows the octet rule!
● An ionic bond forms between oppositely charged ions
○ ionic bond: The association of two atoms resulting from the attraction of opposite charges;
instead of sharing electrons, it’s as if one atom steals from the other (NaCl)
● A chemical reaction involves breaking and forming chemical bonds
○ chemical reaction The process by which molecules are transformed into different molecules.
Atoms retain identity but bonds change.
○ reactant: Any of the starting molecules in a chemical reaction.
○ product: Any one of the transformed molecules that result from a chemical reaction.
2.3: Water: The Medium of Life
● Water is a polar molecule
○ polar: A molecule that has regions of positive and negative charge; readily dissolve in water
(ex: salt)
○ hydrophilic: “Water loving”; describes a class of molecules with which water can undergo
hydrogen bonding.
○ hydrophobic: “Water fearing”; describes a class of molecules poorly able to undergo hydrogen
bonding with water.
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Document Summary
Elements: a pure substance, such as oxygen, copper, gold, or sodium, that cannot be further broken down by the methods of chemistry. Atoms consist of protons, neutrons, and electrons. Nucleus (of an atom): the dense central part of an atom containing protons and neutrons. Proton: a positively charged particle in the atomic nucleus. Electron: a negatively charged particle that moves around the atomic nucleus. Atomic mass: the mass of the atom determined by the number of protons and neutrons. isotopes: atoms of the same element that have different numbers of neutrons. ion: an electrically charged atom or molecule (+ or -). Electrons occupy regions of space called orbitals. Orbital: a region in space where an electron is present most of the time. Shell: an energy level in which an orbital can exist. Note; rutherford"s gold foil experiment: atoms are made up of mostly empty space and a small, densely packed nucleus. Elements have recurring, or periodic, chemical properties.
