Biology Chp 2 Flashcards
The Chemical Context of Life
Compound
chp 2
made of atoms joined by bonds
The number of protons
chp 2
determines an atoms identity
(Oxygen has 8 protons)
An atom’s electron distribution
chp 2
determines its ability to form bonds
A compounds properties
chp 2
depends on its atoms and how they’re bonded together
Matter
chp 2
anything that takes up space and has mass
Element
chp 2
a substance that cannot be broken down to other substances by chemical reactions
Compound
chp 2
a substance consisting of two or more different elements combined in a fixed ratio. Has characteristics different than those of its elements
Essential elements
chp 2
20-25% of the 92 natural elements that an organism needs to live a healthy life and reproduce
humans need 25 but plants only need 17!
Carbon, oxygen, hydrogen, and nitrogen
chp 2
make up about 96% of living matter
Calcium, phosphorous, potassium, sulfur, and a few other elements
chp 2
account for most of the remaining 4% of an organisms mass
other than carbon, oxygen, hydrogen, and nitrogen
Trace Elements
chp 2
required by an organism in only minute quantities
Atom
chp 2
the smallest unit of matter that still retains the properties of an element
Subatomic particles
chp 2
the smallest unit of matter that still retains the properties of an element
- neutrons (no charge), protons (positive), electrons (negative)
Atomic nucleus
chp 2
the protons and neutrons at the center of an atom
Dalton
chp 2
the unit used to measure atoms and subatomic particles
(aka atomic mass unit, amu)
Pro and Neu have masses close to 1 dalton. e- mass is negligible
Atomic number
chp 2
the number of protons an atom has
Written as a subscript to the left of the element’s symbol
The # of e- and pro generally the same
Mass Number
chp 2
the total number of protons and neutrons in the nucleus of an atom
written as a superscript to the left of an element’s symbol
Atomic Mass
chp 2
the total mass of an atom
Isotopes
chp 2
Different atomic forms of the same element
some atoms have more neutrons than others of same element
Radioactive isotopes
chp 2
an isotope in which the nucleus decays spontaneously, giving off particles and energy
radioactive decay used to date fossils
Half-life
chp 2
the time it takes for 50% of the “parent” isotope to decay
each radioactive isotope has a characteristic half-life that is not affected by temp., pressure, or any other environmental variable
Radiometric dating
chp 2
the process used to measure the ratio of different isotopes and calculate how many half-lives(in years) have passed since an organism was fossilized or a rock was formed
Energy
chp 2
The capacity to cause change
Potential Energy
chp 2
the energy that matter posseses because of its location or structure
electrons have potential ebergy due to their distance from the nucleus
Electron potential energy
chp 2
- Greater distance from nucleus means greater potential energy
- an e- potential energy is determined by its energy level
- and e- can only exist at certain evergy levels, not between them
- e- energy level is correlated with its average distance from the nucleus
Electron shells
chp 2
Each have a characteristic ebergy level and distance from the nucleus
- 1st shell: closest to nucleus, lowest potential energy
- 2nd shell: more energy than 1st
- 3rd shell: even more energy
An e- can move from one shell to another but only by absorbing or losing an amount of energy equal to the difference in potential energy between its position in the old shell and that in the new shell.
As an e- absorbs energy, it moves away from the nucleus
As an e- loses energy, it moves closer to the nucleus
Period Table layout
chp 2
top to bottom: increasing e- shells
left to right: addition of e- and protons
e- tend to exist in the lowest available state of potential energy
The first shell cannot hold more than 2 e-
Valence electrons
chp 2
the electrons in the outermost electron shell
Valence shell
chp 2
the outermost electron shell
- an atom with a complete valence shell will not interact readily with other atoms (called inert, or chemically unreactive)
- the chemical behavior of an atom depends mostly on its outermost shell
Electron orbital
chp 2
the 3D space where an electron is found 90% of the time
- 1st shell has one orbital (s)
- 2nd shell has four orbitals; one spherical(2s) and three dumbell-shaped orbitals (2p)
- no more than 2 e- can inhabit a single orbital
- reactivity of an atom arises from presence of unpaired e- in one or more orbitals
Chemical bonds
chp 2
Attractions that hold atoms close together after the transferring and/or sharing of e-
covalent bonds in molecules and ionic bonds in dry ionic compounds are the strongest
Covalent Bonds
chp 2
the sharing of a pair of valence electrons by two atoms
Molecule
chp 2
two or more atoms held together by covalent bonds
Valence
chp 2
the bonding capacity of an atom
usually equals the number of e- required to complete valence shell
Compound
chp 2
Combination of two or more different elements
Electronegativity
chp 2
the attraction of a particular atom for the electrons of a covalent bond
Non-polar covalent bond
chp 2
when 2 atoms have the same electronegativity
Polar covalent bond
chp 2
when the electrons of the bond are not shared equally
Ionic Bonds
chp 2
opposite charges of ions attract one another
Ions
chp 2
when an atom strips another of its electron, resulting in 2 oppositely charged atoms/molecules
Anion
chp 2
a negatively charged ion
Cation
chp 2
a positively charged ion
Ionic Compounds
Salts
chp 2
Compounds formed by ionic bonds
- 3D lattice structure
- Does not consist of molecules, the formula indicates ratios
Hydrogen Bonds
chp 2
the noncovalent attraction between a hydrogen (already covalently bonded) and an electronegtive atom. Weak bonds
Ex.) h-bonds in water between electroneg. oxygen and hydrogen
Van der Waals Interactions
chp 2
the ever changing regions of positive amd negative charge that enable all atoms and molecules to stick to one another. Weak bonds
Biological molecules bind together temporarily only if their
chp 2
shapes are complementary
Molecular shape is determined by
chp 2
the position of orbitals
in a covalent bond, s and p orbitals may hybridize, creating specific molecular shapes
Reactants
chp 2
the starting molecules of a chemical reaction
Products
chp 2
the final molecules of chemical reactions
