Unit 2: Atomic Theory

Question 1

Democritus’ Theory

Answer 1

Democritus believed all matter was made of fire, air, water, and earth. Democritus thought the ratio of these four elements affected the different properties of matter.

Question 2

Atomos

Answer 2

Means indivisible. Democritus called immeasurable small pieces of matter atomos, and he thought they were eternal and couldn’t be destroyed.

Question 3

John Dalton’s 1st Postulate

Answer 3

All elements are composed of tiny indivisible particles called atoms.

Question 4

John Dalton’s 2nd Postulate

Answer 4

Atoms of the same element are identical. The atoms of any one element are different from those of any other element.

Question 5

John Dalton’s 3rd Postulate

Answer 5

Atoms of different elements can physically mix together or chemically combine in simple whole-number ratios to form compounds.

Question 6

John Dalton’s 4th Postulate

Answer 6

Chemical reactions occur when atoms are separated, joined together or rearranged. Atoms of one element are NEVER changed into another element during a chemical reaction.

Question 7

J.J. Thomson’s Atom Model

Answer 7

Called the “Plum Pudding Model” because the positively charged sphere is the pudding and the electrons are the plums spread out through the pudding

Question 8

J.J. Thomson Contribution

Answer 8

Discovered the electron with the cathode ray experiment and he discovered that electrons are negatively charged

Question 9

Ernest Rutherford’s Contribution/Model

Answer 9

Gold Foil Experiment:
1. The atom contained a nucleus that consisted of protons and neutrons and was very dense
2. The electrons of an atom were located outside and surrounded the nucleus
3. Most of the atom is empty space
4. Discovered the proton and its charge

Question 10

James Chadwick’s Contribution

Answer 10

Discovered the neutron

Question 11

Dmitri Mendeleev organized elements according to…

Answer 11

atomic mass

Question 12

Henry Moseley organized elements according to…

Answer 12

atomic number

Question 13

Periodic Law

Answer 13

The appearance of similar properties for elements when arranged in order of increasing atomic number

Question 14

Valence Electrons

Answer 14

Electrons found in the outer shell of an atom. Important because they are the electrons that react with other atoms. Also, they determine the chemical properties of an atom.

Question 15

Group 1 of the Periodic Table

Answer 15

Alkali Metal

Question 16

Group 2 of the Periodic Table

Answer 16

Alkaline Earth Metals

Question 17

Group 3-12 of the Periodic Table

Answer 17

Transition Metals

Question 18

Group 17 of the Periodic Table

Answer 18

Halogens

Question 19

Group 18 of the Periodic Table

Answer 19

Noble Gasses

Question 20

Metals

Answer 20

80% of all known elements
Left and center of the periodic table
Lustrus (shiny)
Malleable (hammer into thin sheets)
Dutile (make into thin wire)
Good conductors of heat and electricity

Question 21

Metalloids

Answer 21

Touch the staircase and have properties of both metals and nonmetals. (Note: Al is a metal!)

They are semiconductors which means they normally do not conduct electricity but will conduct at high temperatures or when certain subjects are added.

Question 22

Nonmetals

Answer 22

Most are located in upper right of periodic table
Most are gaseous at room temperature
Right of the periodic table and hydrogen
Non-lustrous (dull)
Brittle (breaks easily)
Poor conductors (good insulators)

Question 23

The 7 Metalloids

Answer 23

Boron
Silicon
Germanium
Arsenic
Antimony
Tellurium
Astatine

Question 24

Alpha Particles

Answer 24

2 protons and 2 neutrons/He
heavy
positive
3-5 cm
paper; skin
DNA mutation and/or cell death
Can detect smoke

Question 25

Beta Particles

Answer 25

electron
light
negative
2-3 m
glass; metal; water
Can cause cancer and/or cell death
Can be used in cancer treatment

Question 26

Gamma Rays

Answer 26

wave/00y
no mass
neutral
very far (galaxies)
water (large amount); concrete; lead
Can sterilize food

Question 27

Fission

Answer 27

The splitting a heavy nucleus into two nuclei with smaller mass numbers.

Question 28

Fusion

Answer 28

The combining two light nuclei to form a heavier, more stable nucleus.

Question 29

Half-life

Answer 29

The time it takes for one-half of a radioactive isotope to decay.

Question 30

Radioactive Isotopes with Short Half-lifes

Answer 30

Are especially dangerous because they can emit a lot of high energy particles (alpha and beta) and/or electromagnetic radiation (gamma rays) in a short period of time

Question 31

Positron

Answer 31

positive electron

Question 32

Stable Nucleus =

Answer 32

neutrons/atomic # = 1
Closer to 1 = more stable nucleus

Question 33

Alkali Metals

Answer 33

Alkali metals are NEVER found pure in nature; they are too reactive

Reactivity of these elements increases down the group

Question 34

Alkaline Earth Metals

Answer 34

Alkaline earth metals are less reactive than alkali metals

Alkaline earth metals are not found pure in nature; they are too reactive

The word “alkaline” means “basic”

Question 35

Halogens

Answer 35

Halogens are never found pure in nature; they are too reactive

Halogens in their pure form are diatomic molecules (F2, Cl2, Br2, and I2)

Question 36

Noble Gasses

Answer 36

Noble gases are ONLY found pure in nature – they are chemically unreactive

Colorless, odorless and unreactive; they were among the last of the natural elements to be discovered