Hon. Chem Ch. 3 Atoms: The Building Blocks of Matter

Atom

smallest particles of an element that maintains the chemical properties of that element. Neutral when protons= electrons

Law of Conservation of Mass

mass is neither created nor destroyed during ordinary chemical reactions or changes; can only change form

Scientist for Law of Conservation of Mass

Lavoisier

Example of Law of Conservations of Mass

wood burning in a fire; wood changes to ashes, yet still has same mass

Law of Definite Proportions

a single chemical compound contains the same elements in exactly the same proportions by mass, regardless of the size of the sample or the source of the compound

Scientist for Law of Definite Proportions

Proust

Examples of Law of Definite Proportions

sodium chloride(table salt) always consists of 39.34% by mass of the element sodium (Na), and 60.66% by the mass of the element chlorine (Cl);

Water molecule: 2 hydrogen, 1 oxygen atoms = 11% hydrogen and 89% oxygen

Law of Multiple Proportions

if 2 or more compounds are composed of the same 2 elements, then the ratio of the masses of the second element combined with a certain mass of the first element is always a ratio of small whole numbers

Scientist for Law of Multiple Proportions

Dalton

Examples of Law of Multiple Proportions

carbon and oxygen (CO2)
carbon dioxide and carbon monoxide (CO)

Consider samples of each of these compounds, each containing 1.00 g of carbon. In carbon dioxide, 2.66 g of oxygen combine with 1.00 g of carbon. In carbon
monoxide, 1.33 g of oxygen combine with 1.00 g of carbon. The ratio of the masses of oxygen in these two compounds is 2.66 to 1.33, or 2 to 1.

Dalton's Atomic Theory

1) all matter is made of small particles called atoms
2) atoms of an element are identical in size, mass, and other properties*
3) atoms can't be subdivided* , created or destroyed
4) atoms of different elements combine in simple or whole number ratios to form compounds
5) in chemical reactions, atoms are combined, separated, or rearranged

Dalton's Atomic Theory are incorrect now

2) atoms of an element are identical in size, mass, and other properties
3) atoms can't be subdivided

Thomson's Cathode Ray Tube Experiment

Observations:
Rays were deflected away from negatively charged particles

Conclusions:
Particles that composed the cathode ray tube are negatively charged; discovered the electron

Inference based on Thomson's Model

Atoms are electrically neutral, so atoms must contain a positive charge to balance the negative electrons

Milikan's Oil Drop Experiment

Observations:
Measured the charge of an electron

Conclusion:
Scientists used this information and the charge to mass ratio to determine the mass of an electron
(mass of electron is 9.10*10^-28 g)

Inference Based on Milikan's Experiment

Since electrons have almost no mass, atoms must contain other particles that account for the mass of an atom

Rutherford's Gold Foil Experiment

Observations:
1 in 8000 particles were deflected back

Conclusions:
The alpha particles hit something small and dense; discovered nucleus

Nuclear Forces

the interaction that binds protons and neutrons, protons and protons, and neutrons and neutrons together in a nucleus

Proton Charge

+1 (positive)

Proton Mass

1u

Proton symbol

p+

Proton Location

nucleus

Neutron Charge

0 (neutral)

Neutron Mass

1u

Neutron symbol

n

Neutron location

nucleus

Electron charge

-1 (negative)

Electron mass

0

Electron symbol

e^- (e-)

Isotopes

atoms of the same element (same number of protons and electrons) that have different masses (different number of neutrons)

Nuclide

a general term for a specific isotope of an element

Isotopes of Hydrogen

protium, deuterium, tritium

Protium

isotope of hydrogen with 1 proton and 1 amu; stable

Deuterium

isotope of hydrogen with one proton and one neutron in the nucleus; stable

Tritium

isotope of hydrogen with 1 proton, 2 neutrons, 3 amu; radioactive

Hyphen Notation

Element name-mass number; ex. carbon-12

Nuclear Symbol

superscript (mass number), subscript (atomic number) and element symbol

Atomic Number

number of protons and number of electrons

Number of Neutrons

mass number - atomic number

Radioactive Decay

the spontaneous disintegration of a nucleus into a light nuclei, accompanied by particles, electromagnetic, radioactive, or both

Alpha Decay

4/2 He

Alpha Particles

radioactive decay; stopped by paper

Beta Decay

0/-1 e (B)

Beta Particles

stopped by aluminum foil, radioactive decay

Positron Emission

0/+1 e (B)

Positron Particles

stopped by aluminum foil, radioactive decay

Gamma Emission

0/0 y

Gamma Rays

stopped by led barrier, radioactive decay, no mass, energy added, most penetrating

Average Atomic Mass

weighted average of the atomic masses of all naturally

to solve, multiply amu by decimal percent and do it for all of them. then add all of them together w/ correct sigfigs

Mole

the amount of a substance that contains Avogadro's number of particles

Molar Mass

the mass of one mole of a pure substance; units: g/mol

Mole to Atom Conversion (Avogadro's number)

Use 6.022 x 10^23 (Avogadro's number) particles to convert moles to atoms

Mole conversions:

Know how to do:
Moles to mass (g)
Mass (g) to moles

Atom Conversions:

Know how to do:
Moles to atoms
Atoms to moles
Mass (g) to moles to atoms
Atoms to moles to mass (g)