Trace Elements: required by organisms in minute amounts
Essential elements: C, H, O, N (most abundant)
Atom
- “Smallest unit of an element; consists of nucleus of (+) protons and neutrons”
- Electrons orbit the nucleus
- Mostly energy, negligible mass
- Stay at fixed energy level but if absorb energy can move to shell further
- The type of bonds that form between atoms and its strength depends on the electronegativities of atom
- (low to high) nonpolar covalent → polar covalent → ionic
Ionic Bonds
- Form between atoms when electrons are transferred from one atom to another → Forms ions
- Occurs when there is a great electronegativity difference
Covalent Bonds
- Form when electrons are shared; neither atom completely holds electron
- Single covalent, double covalent, and triple covalent bonds form when two, four, and six electrons are shared respectively
Nonpolar Covalent Bonds
- When electrons are shared equally → atoms have same/similar electronegativity
- No charge = hydrophobic
Polar Covalent Bonds
- When electron are shared unequally → atoms have diff electronegativity
- Single water molecule held by polar covalent bonds
- Yes charge = hydrophilic
Hydrogen Bonds
- Weak bonds between molecules; form when (+) charged hydrogen atom in one covalently bonded molecule is attracted to (-) charged area of another covalently bonded molecule → results from polarity
- Strong in large numbers
- Bond holds one water molecule to another water molecule
Vocab
Heat of fusion: energy required to change water from a solid to liquid
Heat of evaporation: energy required to change water from liquid to gas
Mass Number: number of protons and neutrons
Isotopes: atoms of same elements with diff mass/number of neutrons
Electronegativity: measure of an atom’s attraction for electrons
- Allows oxygen to form polar and hydrogen bonds
Energy: capacity to do work
Potential energy: energy that matter has because of location
- Electrons have potential energy because of distance from nucleus
Electron Shell: distance from nucleus where electrons found
- Further = more energy
Valence electrons: outermost electrons
- Determine chemical behavior
Molecule: 2 or more atoms held by bonds
- Molecule shape determined by position of valence electrons orbitals
Compound: two or more different elements joined together chemically