chapter 2 atoms and elements

Question 1

Atoms

Answer 1

• smallest identifiable unit of an element
• about 91 naturally occurring elements
• -about 20 synthetic
• exact # is ambiguous

Question 2

Law of Conservation of Mass

Answer 2

In a chemical reaction, matter is neither created nor destroyed.
* total mass after reaction does not change

Question 3

Law of Constant Composition /definite proportions

Answer 3

all samples of given compound, regardless their source/how they are prepared have same proportions of constituent Element.

Ex: mass ratio: 16g Oxygen/2.0g Hydrogen= 8.0 or 8:1

Question 4

Law of Multiple Proportions:

Answer 4

when 2 elements (A&B) form 2 different compounds, the masses from element B that combine with 1g of element A can be expressed as a ratio of small whole numbers.

EX: CO2 carbon dioxide:
mass O combines with 1g C= 2.67g

CO Carbon monoxide
mass O + 1g C= 1.33g

Mass O to 1g in CO2/Mass O to 1g in CO= 2.76g/1.33g=2.0
ratio: 2:1

Question 5

Atomic Theory (John Dalton, 1808)

Answer 5

1. each E is composed of tiny, indestructible particles called Atoms
2. all atoms of given E have same mass & other properties that distinguish them from atoms of other E
3. atoms combine in simple whole number ratios to form compounds.
4. atoms of one E cant change into another E. in a chem reaction atoms change the way they are bonded together w/ other atoms to form new substance.

Question 6

Cathode Ray

Answer 6

produced when high elec voltage is applied between 2 electrodes w/in a partially evacuated glass tube.
Tube: cathode ray tube

Question 7

electrical charge

Answer 7

negative
fundamental property of some of the particles that compose atoms
attractive/repulsive forces
electrostatic forces

Question 8

Electron

Answer 8

neg. charge low mass particle
present in all atoms
charge: -1.6x10^-19 C

Question 9

Plum Pudding Model- JJ Thompson

Answer 9

Neg charged e- are held together by a (+) charged sphere

Question 10

Radioactivity

Answer 10

emission of small energetic particles from core of certain unstable atoms

Question 11

Rutherford (1871-1937)

Answer 11

Gold foil experiment

• alpha particles to gold foil
• most pass through with no detection
• proved plum pudding model was wrong
• some particles were deflected/ bounced back

Question 12

Nuclear Theory (Rutherford)

Answer 12

1. most atoms mass/pos (+) charge are contained in the core (nucleus)
2. most volume of atom is empty space, throughout which tiny neg (-) electrons are dispersed
3. there are many e- outside of nucleus. (+) particles in nucleus (protons) atom = neutral

Question 13

Neutrons

Answer 13

neutral particles in nucleus

Question 14

Atomic Mass Unit (amu)

Answer 14

1/2 mass of C atom
containing 6 protons & 6 neutrons
*mass of 1 p or n = 1 amu
*proton (p)= 1.67262x10^-27 kg (+1 relative charge)
*neutron (n)= 1.674493x10^-27 kg (0 rel charge)
*electron (e-)= .00091x10^-27 kg (-1 rel charge)

Question 15

Atomic Number

Answer 15

# of protons in atom nucleus
defines element

Question 16

Chemical Symbol

Answer 16

one or two letters abbreviated for element

- listed below atomic # on periodic table

Question 17

Isotopes

Answer 17

atoms w/ same number of protons but different # of neutrons

Question 18

Natural Abundance

Answer 18

relative % of particular isotopes in a naturally occurring sample w/ respect to other isotopes of same element

Question 19

Mass number

Answer 19

sum of protons and neutrons

Question 20

Ions

Answer 20

losing or gaining electrons (e-)

Question 21

Cations

Answer 21

positivly charged ions
lose electrons

EX: Li+

Question 22

Anions

Answer 22

Negatively charged ions
gain electrons

EX: F-

Question 23

Periodic law

Answer 23

when elements are arranged in order of increasing mass, certain sets of properties recur periodically

• mass increases left to right
• rows = similar properties

Question 24

Metals

Answer 24

left side/ middle period

• Properties: good conductors of heat/ electricity
• can be pounded into flat sheets
• drawn into wires
• often shiny
• tend to lose e- in chem reactions
• properties tend to be less predictable based on location

Question 25

Non metals

Answer 25

upper right side
varied properties
poor conductors of heat/ electricity
tend to gain e- when undergo chem reaction

Question 26

Metalloids

Answer 26

some= semi conductors
mixed properties
intermediate elec. conductivity

Question 27

Main group elements

Answer 27

properties tend to be largely predictable based on position on periodic table

Question 28

Family

Answer 28

column w/in main group

Question 29

Nobel Gases

Answer 29

• group 8a
• mostly unreactive
• chemically stable

Question 30

Alkali Metals

Answer 30

• reactive metals
• group 1A

EX: Na is violent when in water

Question 31

Alkaline Earth Metals

Answer 31

• group 2A

- reactive but not as much as group 1A

Question 32

Halogens

Answer 32

• group 7A
• very reactive non metals

ex: Cl (chlorine)

Question 33

Atomic Mass

Answer 33

calculated average mass

- average mass of isotopes that compose element “weighted according to natural abundance of each isotope”

Question 34

Mole

Answer 34

amount of material containing
6.022x10^23 particles
(Avogadro’s number)
-value of mole = number of atoms in exactly 12g C of pure C-12
-relationship between mass & # of atoms
-count atoms by weighing them

conversions :

1mol/ 6.022x10^23 atoms or 6.022x10^23 atoms/ 1mol

Question 35

Molar Mass

Answer 35

mass of 1 mol of atoms of an element

measurement = g/mol is numerically equal to atomic mass in amu

Question 36

Scanning Tunneling Microscopy

Answer 36

• image and move individual atoms/ molecules

- extremely sharp electrode over surface & measuring the resulting “tunneling current”