Atoms, Molecules, Ions, and water Flashcards
Notations for Atoms
X = element Symbol A = Atomic mass number = # of proton + # of neutrons Z= Atomic # = # of protons = # of electrons in a neutral atom.
Dalton’s Atomic Theory
- Each element made up atoms
- Atoms in an elements are identical
- Chemical compounds form when atoms of different element combine with each other
- Chemical reaction = reorganization of atoms
Isotopes
Atoms with same atomic number (z) but different mass number (A)
has a different # of Neutrons
Element
Pure substance with only one type of atoms
eg. Ag, Mg, Fe
Eg2. H2, N2, O2
Compound
Pure substance with two or more different atoms
Molecules
Combination of atoms
Represented by chemical formulae
Eg. CO2, H2O
Anion
Negatively charged molecule/element (-)
Eg. Cl-
Cation
Positively charged molecule/element(+)
Eg. Na+
Atomic mass spectrometry
separates ions by mass-to-charge ratio
Atomic mass
Based all on Carbon 12
Mol
1 mol = 6.022 x 10e23
Molar Mass
Mass in g of 1 mole of that substance
Mass percent
the mass of an element in a compound expressed as a % of the total mass of the compound
Molecular Formula
exact # of atoms in one molecule of the compound
Eg. C2H6Br2
Empirical formula
the formula that expresses the smallest whole number ratio of atoms in a compound
Eg. CH3Br
Empirical formula calculation
- burn sample in the presence of O2: convert C to CO2 and H to H2O:
- determine the % of carbon and hydrogen
from the masses of CO2 and H2O - calculate # of moles from the elemental masses based on a 100g sample
- divide each mole by the smallest #.
Limiting reactant
The limiting reactant or limiting reagent is a reactant in a chemical reaction that determines the amount of product that is formed.
Percent yield
change conditions of the reaction and monitor an increase or decrease in the % yield
Theoretical yield
“predicted” amount of product Theoretical yield is dictated by limiting reagent
Actual yield
Reality: obtained less than Theoretical yield
Percent yield
Actual yield(g) / theoretical yield (g) x 100%
Solving stoichiometric questions
- Balance equations
- Convert known mass to mol
- Determine limiting reagent
- Use limiting reagent to determine mol of desired product
- Convert mol to grams
Water
Polar covalent bond
Difference in electronegativity between O and H
Bonding electron pairs are shared unevenly
Water
O atoms has 2 lone pairs: difference b/w lone pairs and H atoms result in a bent structure.
Electronegativity
Atom’s tendency to attract electrons
Increase as you go across
Decrease as you go down
Polar Solvents
Dissolves ionic solids by forming a shell around the ion
Process of solvation
Hydration
Ionic solids forming a shell around the ion
Solvation of water.
3 groups of polar substances based on electroconductivity
- Strong electrolytes: Compounds that are completely ionized in a solution. Eg. Soluable salts & strong Acid/base
- Weak Electroyltes: Compounds that only partially ionizes in solution
- Non-electrolytest: Substance that are solvable but do not ionize. Eg. sugar, alcohol.
Molarity
Mol/L
