Khan Academy: Chemistry

Electrolytes

Certain ions are necessary for nerve impulse conduction, muscle contractions and water balance. (i.e. sodium, potassium)

Ions

Charged particles formed when atoms lose/gain electron(s)

Equilibrium constant

Each reaction has its own characteristic equilibrium point, which we can describe with a number

Order of the periodic table

Elements are placed in order on the periodic table based on their atomic number, how many protons they have

Law of conservation of matter

Equations must be balanced; no atoms are created or destroyed over the course of a normal chemical reaction

Isotopes

Forms of the same atom that differ only in their number of neutrons

Inert/noble gases

Helium, neon, and argon, as group 18 elements, have outer electron shells that are full or satisfy the octet rule. This makes them highly stable as single atoms, and have non-reactivity

Hydrogen bonds

In a polar covalent bond containing hydrogen (e.g., an O-H bond in a water molecule), the hydrogen will have a slight positive charge because the bond electrons are pulled more strongly toward the other element. Because of this slight positive charge, the hydrogen will be attracted to any neighboring negative charges. They are common, and water molecules in particular form lots of them. Individual hydrogen bonds are weak and easily broken, but many hydrogen bonds together can be very strong.

Octet Rule

In general, atoms are most stable, least reactive, when their outermost electron shell is full. Most of the elements important in biology need eight electrons in their outermost shell in order to be stable

Determining polar vs. nonpolar covalent bonds

In general, the relative electronegativities of the two atoms in a bond - that is, their tendencies to "hog" shared electrons - will determine whether a covalent bond is polar or nonpolar. Whenever one element is significantly more electronegative than the other, the bond between them will be polar, meaning that one end of it will have a slight positive charge and the other a slight negative charge.

Radioisotopes

Isotopes that emit, or kick out, subatomic particles to reach a more stable, lower-energy, configuration

Anions

Negative ions are formed by electron gain. Anions are named using the ending "-ide": for example, the anion of chlorine is called chloride.

Purpose of the Periodic Table

Similar to a filing system. The position of each element in the table gives important information about its structure, properties, and behavior in chemical reactions. Specifically, an element's position in the periodic table helps you figure out its electron configuration, how the electrons are organized around the nucleus. Atoms use their electrons to participate in chemical reactions, so knowing an element's electron configuration allows you to predict its reactivity—whether, and how, it will interact with atoms of other elements.

Strong vs. weak bonds

Strong: covalent and ionic bonds Weak: hydrogen bonds and London dispersion forces Both strong and weak bonds play key roles in the chemistry of our cells and bodies. For instance, strong covalent bonds hold together the chemical building blocks that make up a strand of DNA. However, weaker hydrogen bonds hold together the two strands of the DNA double helix. These weak bonds keep the DNA stable, but also allow it to be opened up for copying and use by the cell.

Atomic Mass

The atomic mass of a single atom is simply its total mass and is typically expressed in atomic mass units or amu. By definition, an atom of carbon with six neutrons, carbon-12, has an atomic mass of 12 amu. In general, an atom's atomic mass will be very close to its mass number, but will have some deviation in the decimal places.

Electron configuration

The first electron shell, 1n, corresponds to a single 1s, orbital. The 1s, orbital is the closest orbital to the nucleus, and it fills with electrons first, before any other orbital. For example, Hydrogen can be written as 1s^1, where the superscripted 1 refers to the one electron in the 1s orbital

Mass Number

The number of protons and the number of neutrons. If you want to calculate how many neutrons an atom has, you can simply subtract the number of protons, or atomic number, from the mass number.

Protons

The number of protons in the nucleus determines which element an atom is

Electron shell numbers

The shell closest to the nucleus, 1n, can hold 2 electrons, while the next shell, 2n, can hold 8, and the third shell, 3n, can hold up to 18.

Equilibrium

This back and forth continues until a certain relative balance between reactants and products is reached. At equilibrium, the forward and backward reactions are still happening, but the relative concentrations of products and reactants no longer change.

Electron subshells

We can break each electron shell down into one or more subshells, which are simply sets of one or more orbitals. Subshells are designated by the letters s, p, d, and f, and each letter indicates a different shape.

Electron transfer

When one atom loses an electron and another atom gains that electron

van der Waals forces

a general term for intermolecular interactions that do not involve covalent bonds or ions; hydrogen bonds and London dispersion forces are examples of this

Relative Atomic Mass

an average of the atomic masses of all the different isotopes in a sample, with each isotope's contribution to the average determined by how big a fraction of the sample it makes up. The relative atomic masses given in periodic table entries—like the one for hydrogen, below—are calculated for all the naturally occurring isotopes of each element, weighted by the abundance of those isotopes on earth.

Matter

anything that occupies space and has mass

Covalent bonds

atoms can become more stable is by sharing electrons (rather than fully gaining or losing them). more common than ionic bonds in the molecules of living organisms.

Ionic bonds

bonds formed between ions with opposite charges. For instance, positively charged sodium ions and negatively charged chloride ions attract each other to make sodium chloride, or table salt.

Irreversible reactions

chemical reactions simply run in one direction until the reactants are used up

Molecules

collections of atoms held together by chemical bonds

Electron orbitals

electrons don't really circle the nucleus, but rather spend most of their time in sometimes-complex-shaped regions of space around the nucleus

Nonpolar covalent bond

form between two atoms of the same element, or between atoms of different elements that share electrons more or less equally. For example, molecular oxygen O2 is nonpolar because the electrons are equally shared between the two oxygen atoms.

Reversible reactions

go in both the forward and backward directions: reactants turn into products, but products also turn back into reactants

Elements

have specific chemical and physical properties and cannot be broken down into other substances through ordinary chemical reactions. Gold, for instance, is an element, and so is carbon.

Radioactive atoms

have unstable nuclei, and they will eventually release subatomic particles to become more stable, giving off energy—radiation—in the process

Electronegativity

how badly wants to "hog" electrons; the power of an atom in a molecule to attract electrons to itself

Coefficients

how many of each molecule participate in the reaction; written before the elements in a chemical reaction

Electron affinity

how much they "want" electrons

Electrons

negatively charged particles that orbit around the nucleus; the number of electrons surrounding the nucleus determines which kind of reactions the atom will undergo

Valence shell

outermost shell of an atom; the number of electrons in the outermost shell of a particular atom determines its reactivity, or tendency to form chemical bonds with other atoms.

Cations

positive ions formed by losing electrons

Reactants

substances that go into a chemical reaction

Atomic Nucleous

the center of the atom and contains positively charged particles called protons and neutral, uncharged, particles called neutrons

Polar covalent bond

the electrons are unequally shared by the atoms and spend more time close to one atom than the other. Because of the unequal distribution of electrons between the atoms of different elements, slightly positive (δ+) and slightly negative (δ-) charges develop in different parts of the molecule.

Atomic number

the number of protons in an atom

Isotope's Half-Life

the period over which half of the material will decay to a different, relatively stable product

Decay

the process in which radioisotopes release particles and energy

Atom

the smallest unit of matter that retains all of the chemical properties of an element. The attraction between the positively charged protons and negatively charged electrons holds the atom together

Products

the substances produced at the end of the reaction

London dispersion forces

weak attractions between molecules. However, unlike hydrogen bonds, they can occur between atoms or molecules of any kind, and they depend on temporary imbalances in electron distribution.

Chemical reactions

when chemical bonds between atoms are formed or broken