Section 1.2 Flashcards
Element
Simplest type of matter that has unique chemical properties
- made up of one type of atom
- each element is unique
Ex. H,C, He, O, etc.
Molecule
Independent structures made up of at least 2 atoms BONDED together
Ex. H2, CH4, CH3OH
Compound
Occur when at least 2 different molecules or elements are bonded together
Ex. NaCl, NH4Cl
Mixture
2 or more chemical substances that are physically mixed/combined but NOT bonded together
Ex. Air → ~78% N2, ~20% O2, ~2% other
Chemical Reactions
Process that lead to a transformation (change) or chemical substance
→ New bonding
Ex. C + O2 → CO2
Atomic theory → Four important postulates (assumed existence or truth):
1) All matter consists of atom: atoms cannot be created or destroyed
2) Atoms of one element cannot be changed into atoms of another element (Pb → Ae - NOT possible)
3) Atoms of a given element are all the same (same mass and same internal structure)
4) compounds tended to form molecules in chemical reactions with specific ratios: N2 + 3H2 → 2NH3
Mass laws
Mass is conserved (cannot be created or destroyed)
A specific compound is composed of the same element in the same parts (fractions) by mass
Specific elements react to form compounds that combine with fixed masses that can be expressed as a ratio of small whole numbers
The Nuclear Atom Model
The process of uncovering the components that make up an atom involved a series of historical experiments:
Cathode Ray: electrical discharge consists of negatively charged particles
“Cathode ray particles” = electrons
- electrons can be generated from many different types of matter (electrons are a components in all matter)
Mass/Charge Ratio:
The mass of an electron is 1/1600 the mass of the lightest elements (H)
Charge of an Electron: determined by Millikan oil-drop experiment (1909)
1) Fine mist of oil spayed into apparatus
2) Oil droplets fall through hole in positively charged plate
3) X-ray knock electrons from surrounding air, which stick to droplets
4) Electrically charged plates influence droplet’s motion
5) Observer times droplet’s motion and controls electric field
The total charge on the oil droplets is always integer number of electron on the particle
Charge of electron = -1.602 x 10^-19C
Atomic Nucleus: Rutherford (1910) contradicted the “plum-pudding” model for atoms
Most of the atom is empty space
Nucleus is positively charged, diffuse in the center of the atom
Proton
P+
positively charged +1.602 x 10^-19 C
Weight: 1.673 x 10^-24 g = 1 AMU
Neutron
n
no charge
Weight: Weight: 1.675 x 10^-24 g = 1 AMU
Electron
e-
negatively charged particle
Weight: 9.109 x 10^-28 g =n 0 AMU
Atomic Number
Z
number of protons in an atom
defines the element
