Final Exam Flashcards
Allotropes
Allotropes: different forms of same element
Pure substance:
constant & uniform composition
Pure substance: ELEMENT vs. COMPOUND
Element: molecules contain only 1 type of atom [O2]
Compounds: combining different atoms [H2O] –> can be decomposed into 2+ atoms
Mixture:
2+ types molecules can be separated by physical changes (ie. evaporation)
Mixture: Homogenous vs Heterogeneous
Homogenous mixture: uniform composition - solutions & air (“solution” ie. air)
Heterogeneous mixture: composition varies from point to point
Physical properties:
observed without changing substance into another, reversible
(mass, volume, density, boiling pt, solubility, color)
Physical properties: intensive vs extensive
Intensive: independent amount substance (boiling pt, density, color)
Extensive: depend amount substance (weight, mass, length)
Chemical properties:
undergoes change chemical composition
(flammability, corrosiveness, reactivity with acid)
Key words: reacting, changing, burning
Changes in matter: physical vs chemical
Physical change: don’t change composition of substance and no new substance is formed (wax melts, magnetizing solids)
Chemical change: result in formation of new substance with different chemical properties (combustion, oxidation)
Significant figure rules
All non-zero digits = significant
Zeros:
Left = not significant
Middle = significant
Right = significant after decimal point
Rounding numbers rules
Adding/subtracting: same # decimal places as the # with least decimal places
Multiplying/dividing: same # of digits as # with least sig figs
If digit dropped < 5 (round down) if > 5 (round up)
If digit dropped = 5 (round up or down whichever yields an even value for the retained digit)
Accuracy
Precision
Exact numbers
Accuracy: variation from accepted value
Precision: how similar results are when repeated in the same manner
Exact numbers: counting, definition, unit conversion (infinite # sig figs, no uncertainty)
Density
desnity = mass / volume
[g/ml = g/cm^3]
Used to identify unknown substance
Determine density of irregular object: use volume water displaced in beaker
Atom
Atom: smallest unit of an element that can participate in chemical change (indivisible)
Element vs molecule
Element: 1 type of atom, in which mass is a characteristic feature
Molecule: 2+ atoms joined by chemical bonds
Dalton’s atomic theory:
WRONG, but laid foundation for future work
- All matter is made up of tiny particles called atoms (indivisible & indestructible)
- Atoms given element are identical in size, mass, chemical properties
- Atoms combine to form compounds in whole number ratios
- Atoms of element cannot change into atoms another element (only rearrange)
Cathode ray tube, J.J. Thomson
DISCOVERED: electrons negative, charge to mass ratio
Plum pudding model atom
Oil drop experiment, Millikan:
DISCOVERED charge of an electron
Alpha-ray scattering, Rutherford
DISCOVERED nucleus in atoms (disprove plum pudding)
Nucleus has protons & neutrons (which are much much heavier than electrons) → nucleus accounts for most of an atom’s mass but very little of its size
Rutherford’s model of atom:
- 3 main points
- limitations
- All + charge & mass concentrated inside nucleus (tiny region)
- Negatively charged particles revolve around nucleus in circular path
- Electrostatic force attraction between proton & electrons holds atom together
LIMITATIONS: failed to explain
- Stability of an atom
- Electronic structure of atom (how electrons arranged inside nucleus)
Atomic number (Z):
protons in nucleus (found in periodic table)
Neutral atom: electrons = protons = Z
Mass number (A):
protons + neutrons
Nuclear symbol:
represents nucleus of an isotope
Atomic number (Z): protons
Mass number (A): protons + neutrons
Empirical formula:
molecular formula expressed in lowest whole number ratio
