ch. 3 - the building blocks of matter

Question 1

law of conservation of mass

Answer 1

mass is neither created nor destroyed during ordinary chemical reactions or physical changes

Question 2

law of definite proportions

Answer 2

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

Question 3

law of multiple proportions

Answer 3

if two or more different compounds are composed of the same two 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

Question 4

Dalton’s Atomic Theory

Answer 4

• all matter is composed of extremely small particles called atoms
• atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties
• atoms cannot be subdivided, created, or destroyed
• atoms of different elements combine in simple whole number ratios to form chemical compounds
• in chemical reactions, atoms are combined, separated, or rearranged

Question 5

Modern Atomic Theory (compared to Dalton’s)

Answer 5

revised & corrected aspects:

• atoms ARE divisible into even smaller particles
• a given element CAN have atoms with different masses

unchanged aspects:

• all matter is composed of atoms
• atoms of any one element differ in properties from atoms of another element

Question 6

atom

Answer 6

the smallest particle of an element that retains the chemical properties of that element

Question 7

nucleus

Answer 7

a very small region located at the center of an atom

Question 8

what are the three subatomic particles and their properties?

Answer 8

proton:
- positively charged particles in the nucleus
- relative electric charge of +1
- mass number of 1

neutron:
- neutrally charged particles in the nucleus
- relative electric charge of 0
- mass number of 1

electron:

• negatively charged particles in region surrounding nucleus
• relative electric charge of -1
• mass number of 0

Question 9

cathode-ray tube experiments

Answer 9

• Joseph Thomson
• measured the charge-to-mass ratio of an electron
• composed of negatively charged particles

Question 10

oil drop experiment

Answer 10

• Robert Millikan

- measured the charge of the electron

Question 11

gold foil experiment

Answer 11

• Ernest Rutherford
• led to discovery of densely packed bundle of matter with a positive charge (nucleus)
• some alpha particles were deflected by tiny nucleus while most passed through undisturbed

Question 12

nuclear forces

Answer 12

short-rang proton-neutron, proton-proton, and neutron-neutron forces that hold nuclear particles together

Question 13

picometers

Answer 13

used to measure atomic radii (center of nucleus to outer portion of electron cloud)

Question 14

average atomic mass

Answer 14

a weighted average of the masses of the naturally occurring isotopes of that element

Question 15

atomic number

Answer 15

the amount of protons of each atom of that element

Question 16

mass number

Answer 16

a combination of protons and neutrons of atoms in the element

Question 17

isotopes

Answer 17

• atoms of the same element that have different masses

- isotopes of a particular element all have the same number of protons and electrons but different numbers of neutrons

Question 18

hyphen notation

Answer 18

the mass number written with a hyphen after the name of the element (uranium-235)

Question 19

nuclear symbol

Answer 19

the superscript that indicates the mass number and the subscript that indicates the atomic number

Question 20

nuclide

Answer 20

a general term for a specific isotope of an element

Question 21

mole (mol)

Answer 21

the amount of a substance that contains as many particles as there are atoms in exactly 12g of carbon-12

Question 22

Avogadro’s number

Answer 22

6.022 x 10^23 –> the number of particles in exactly one mole of a pure substance

Question 23

molar mass (g/mol)

Answer 23

the mass in grams of a pure substance

-numerically equal to the atomic mass