Chapter 2 - The Chemical Context of Life Flashcards
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.
Trace elements
An element indispensable for life but required in extremely minute amounts.
Atom
The smallest unit of matter that still retains the properties of an element.
Neutrons
A subatomic particle with no electrical charge.
Protons
A subatomic particle with a positive electrical charge.
Electrons
A subatomic particle with a negative electrical charge. Form a cloud around the nucleus.
Atomic nucleus
Contains protons and neutrons. Almost the same mass and are measured in Daltons.
Daltons
A measure of mass for atoms and subatomic particles; the same as the atomic mass unit, or amu.
Atomic number
The number of protons in an atom, unique for each element and designated by a subscript to the left of the elemental symbol.
Atomic mass
The total mass of an atom, which is the mass in grams of 1 mole of the atom.
Mass number
The sum of the number of protons and neutrons in an atoms nucleus.
Isotope
One of several atomic forms of an element, each with the same number of protons but a different number of neutrons, thus differing in atomic mass.
Radioactive Isotope
An isotope that is unstable; the nucleus decays spontaneously, giving off detectable particles and energy.
Some applications of radioactive isotopes in biological research are
- Dating fossils
- Tracing atoms through metabolic processes
- Diagnosing medical disorders
Potential energy
The energy that matter has because of its location or structure
Electron shell
An electron’s state of potential energy. Also called energy level.
The chemical behavior of an atom is determined by…
valence electrons.
Valence electrons
Electrons in the outermost electron shell, or valence shell.
Elements with a full valence shell are…
Chemically inert
Orbital
the three-dimensional space where an electron is found 90% of the time.
Chemical bond
An attraction between two atoms, resulting from a sharing of outer-shell electrons or the presence of opposite charges on the atoms. The bonded atoms gain complete outer electron shells.
Covalent Bond
A type of strong chemical bond in which two atoms share one or more pairs of valence electrons. Can form between atoms of the same element or atoms of different elements
Molecule
Two or more atoms held together by covalent bonds.
Single (covalent) bond
The sharing of one pair of valence electrons.
Double (covalent) bond
The sharing of two pairs of valence electrons.
Structural formula
The notation used to represent atoms and bonding. For example, Hydrogen with its single bonded two valence electrons: H—H or H:H
Compound
A combination of two or more different elements.
Valence
The bonding capacity of a given atom; usually equals the number of unpaired electrons required to complete the atoms outermost (valence) shell.
Electronegativity
An atom’s attraction for the electrons in a covalent bond.
The more electronegative an atom, the more ________ it pulls shared electrons toward itself.
strongly
Nonpolar covalent bond
A type of covalent bond in which electrons are shared equally between two atoms of similar electronegativity.
Polar covalent bond
A type of covalent bond between atoms that differ in electronegativity. The shared electrons are pulled closer to the more electronegative atom, making it slightly negative and the other atom slightly positive.
Ionic Bond
A chemical bond resulting from the attraction between oppositely charged ions. (One atom steals an electron from the other atom so that both have completed valence shells).
Ion
An atom or group of atoms that has gained or lost one or more electrons, thus acquiring a charge.
Cation
A positively charged ion.
Anion
A negatively charged ion.
Ionic bond
An attraction between an anion and a cation. Compounds formed by ionic bonds are called ionic compounds, or salts .
Weak chemical bonds
Reinforce shapes of large molecules and help molecules adhere to each other. Examples are ionic bonds and hydrogen bonds.
Hydrogen bond
A type of weak chemical bond that is formed when the slightly positive hydrogen atom of a polar covalent bond in one molecule is attracted to the slightly negative atom of a polar covalent bond in another molecule or in another region of the same molecule.
Van der Waals Interactions
Weak attractions between molecules or parts of molecules that result from transient local partial charges. Collectively, such interactions can be strong, as between molecules of a gecko’s toe hairs and a wall surface.
A molecule’s shape is determined by…
The positions of its atoms’ valence orbitals. In a covalent bond, the s and p orbitals may hybridize, creating specific molecular shapes. Biological molecules recognize and interact with each other with a specificity based on molecular shape, so molecules with similar shapes can have similar biological effects.
Chemical reactions
The making and breaking of chemical bonds. All chemical reactions are reversible: products of the forward reaction become reactants for the reverse reaction.
Reactants
The starting molecules of a chemical reaction.
Products
The final molecules of a chemical reaction.
Chemical equilibrium
Reached when the forward and reverse reaction rates in chemical reactions are equal.
