Gen Chem 1: Chapter 2: Atoms

Law of Conservation of Mass

matter is neither created nor destroyed

Law of Constant Composition

a pure compound always has same composition

A 11.59 sample of NaBr contains 22.34% of Na by mass. How many grams of sodium does a 8.87g sample of sodium bromide contain?

Due to Law of Constant Composition, Na will always have 22.34% by mass in NaBr

8.87 (0.2234) =1.98

Law of Multiple Proportions

relationship between different compounds composed of same two elements

ex: CO₂ has twice as much oxygen per carbon, as does carbon monoxide

Dalton’s 5 Postulates

1. all matter is composed of atoms

2. atoms have unique characteristics and behavior

3. atoms combine in whole number ratios to form compounds

4. atoms retain their identity in chemical reactions

5. atoms aren’t lost in chemical reactions, they rearrange

Dalton’s False Postulates

1. atoms are indivible and indestructible

2. atoms of any given elemnt are identical in size, mass, chemical properties

metals

1. solid at standard state (except mercury - liquid)

2. malleable & ductile (stretched into thin wire)

3. conduct heat + electricity

nonmetals

1. can be solid, liquid, or gas in standard state

2. solid nonmetals are brittle

metalloids

1. brittle (like nonmetals)

2. shiny & metallic (like metlas)

3. conduct heat + electricity LESS than METALS but MORE than NONMETALS

metallic character (increase/decrease) going down the group

metallic character (increase/decrease) going across periods

metallic character increase going down the group

metallic character decrease going across periods

more metallic means it _____ its ______ more readily - more ready to become a metal

loses its electrons more readily

metallic character increase means its (harder/softer)

softer

alkali metals

Group 1A

1. soft, shiny

2. react violently w/ air and moisture (water)

alkaline earth metals

Group 2A

1. harder than alkali metals

2. LESS reactive than alkali metals

3. burn brightly with oxygen

chalcogens

Group 6A

1. oxygen group

2. vary from gases to metalloids to metals going down the group

halogens

Group 7A

1. diatomic elements

2. vary from gases (F₂, Cl₂) to liquids (Br₂)

noble gases

Group 8A

1. unreactive

2. monatomic gases

atomic mass

1 u = 1.6605 × 10^-27 kg

^{the bottom number on the periodic table element}

Coulomb’s Law

force of attraction/repulsion btwn 2 particles

1. directly proportional to size of 2 charges

2. inversely proportional to the square of the distance between

Volta’s Battery

• plates of zinc & copper separated by cardboard soaked in sulfuric acid produced an electric current

• first controlled source of electric energy

• found that electrical energy can break compounds into elements

Thomson’s Cathode Ray Tube

Findings:

1. first subatomic particle

2. charge-to-mass ratio of electron

3. beam of electrons can be modulated by electric fields

Thomson’s Plum Pudding Model

positive charge surrounding most of atom & electrons embedded

ex: blueberry muffin

• pos charge: cakey base

• electrons: blueberries

Millikan’s Oil Drop Experiment

found charge on electron

Rutherford’s Gold Foil Experiment

• to test Thomson’s Plum Pudding Model

• expected heavy alpha particles to pass striaght through gold foil — it deflected

  • alpha particles struck the nucleus and deflected

• found the nucleus

nucleus of an atom

• postively charged

• made up of protons and neutrons

• in natural state, the number of protons is equal to the number or electrons

• heavy and dense

True or False: The number of nucleons present in the nucleus is equal to the numebr of electrons present outside the nucleus.

False - electrons can be some number of protons only - nucleons refers to protons + neutrons

True or False: The nucleus can be positively or negatively charged depending on the identity of the atom.

False - the nucleus can NEVER be negatively charged

List the subatomic particles from HEAVIEST —> LIGHTEST

1. neutron

2. proton

3. electron

atomic number

number of PROTONS (identifies the atom [element])

mass number

number of PROTONS + number of NEUTRONS

isotope

refers to the atom

SAME number PROTONS, DIFFERENT number of neutrons

SAME atomic number, DIFFERENT mass number

nuclide

top number - mass number (protons + neutrons)

bottom number - atomic number (protons)

average atomic mass (u)

weighted average of different isotopes of the element

formula mass (molecular mass/weight)

mass of a single molecule or formula unit

ex: CO₂

1(12.01 u) + 2(16.00) = 44.01 u

Percent Composition

When converting between grams to moles, use ____ ____

molar mass

When converting between moles and atoms/molecules use____ _____

Avogadro’s Number = 6.022 × 10²³