Chapter 2
Matter
Organisms made of matter
- anything that has mass
element: cannot be broken down into simpler form
compound: substance made up of two or more different elements
trace elements: important to life, but are found in very small amounts
Hydrogen, Carbon, Nitrogen, Oxygen, make up 96% of life
Atoms: building block of matter
made up of neutrons, electrons, protons
- dalton: mass of neutron/proton
atomic number: number of protons
- atoms neutral by default, so protons = electrons
- # of neutrons -> mass - atomic number
isotopes: different # of neutrons
- different mass
- can be radioactive; used as tracers in medicine
- half life: time takes to decay 50%
- used in radiometric dating to find age of fossil or rock
Electrons are organized in separate energy levels
- electron shells
- atom’s behavior depends on valence shell
- dictate atom’s
bonding
Bonds
Covalent Bonds: atoms share electrons
- single bond: both contribute one electron, forming one pair
- double bond: both contribute two, forming two pairs
- valence: bonding capacity
- ex: since Carbon has 4 valence electrons, it can make up to 4 covalent bonds
- electronegativity: atoms attract the electrons in the covalent bond
- ex: H2O, since O is more electronegative, it pulls bonds towards it, thus bent
shape
- when electronegativity is same in the compound: nonpolar covalent bond
- electronegativity is different, one atom pulls electrons stronger: polar covalent
bond
- ex: H2O
Ionic Bonds: atoms gives electron to other
- atom with more electronegativity takes electron from other
- result: two opposite charged atoms (ions)
- + charge: cation
- - charge: anion
- metal + nonmetal
- salts are formed
- ex: Na and Cl becomes Na+ and Cl-
(salt)
Hydrogen Bonds:
1. hydrogen covalently bonds to electronegative atom
2. hydrogen becomes slightly positive
3. hydrogen attracts other electronegative atoms (usually Oxygen)
- normally weak, but incredibly strong in huge numbers (ex. H2O)
- crucial to life, gives water its
properties
Van der Waals:
- because electrons aren’t always evenly distributed, regions of + or - charge can form
- very weak
- but similar to H-bond: strong in large numbers
Molecular Shape
- most molecules with >2 atoms have nonlinear shapes
- for atoms with electrons in s and p orbitals, forms tetrahedron shape
- shape determines how molecules interact with each other
- they can only bind if their shapes are complementary