Atomic Theory of Matter

Question 1

what is dalton’s atomic theory

4

Answer 1

1. element= made of atoms
2. atoms of same element=same; atoms of different element=different
3. atoms cannot be created/destroyed; element cannot change to another element
4. compunds=more than 1 element combine; same relative number & kind of atoms (balancing eq)

Question 2

important laws in the atomic theory of matter

3

Answer 2

law of conservation of mass (antoine lavoisier)
law of definitie composition (joseph louis proust)
law of multiple proportions (john dalton)

Question 3

what is the law of conservation of mass

3

Answer 3

• by antoine lavoisier
• matter is not created nor destroyed during chem/physical reactions
• total mass of reactants=total mass of products

Question 4

what is the law of definite composition

2

Answer 4

• by joseph louis proust
• given compound has elements in constant composition and proportion (limiting & excess reactants)

Question 5

what is the law of multiple proportions

Answer 5

if two elements form more than 1 compound, masses of A & B are in ratio of small whole numbers (NO, NO2, N2O, N2O2,N2O5)

Question 6

what is the electron

Answer 6

by JJ Thompson in 1897 using cathode ray tubes (initially called corpuscules)

Question 7

what is the cathode ray expeiment

3

Answer 7

• cathode rays= beams that travel from - to + electrode
• if near electric field, ray was repelled by the negative pole and it was deflected towards the positive pole=cathode ray is negatively charged (- and - repel)
• used this & adjusted electrical field strength for beam to travel undeflected; charge-to-mass ratio of electron=-1.76 x 108 C g-1

Question 8

what is radioactivity

2

Answer 8

• by ernest rutherford
• 3 types of radiation: alpha(+), beta(-), gamma(neutral)

Question 9

what is electron’s charge

Answer 9

• by Robert Milikan thru Milikan’s Oil Experiment
• 1909= charge of electron is 1.602x10 -19 C thru JJ Thompson’s charge-to-mass ratio of -1.76 x10 8 C g-1
• electron mass=9.10 x 10 -28

Question 10

what is the Milikan’s Oil Drop Experiment

2

Answer 10

• oil droplets with net negative charge thru xray irradiation pass thru electrically charged plates which can slow down/speed up the fall of particles when voltage is varied depending on distance between droplets
• calculated from oil droplets that the charge is 1.602 x 10 -19 C

Question 11

what is radioactivity

3

Answer 11

• by henri becquerel in 1896
• uranium spontaneously emits radiation (radioactivity)
• marie & pierre curie started to identify and isolate source of radiation of uranium

Question 12

who is william ramsay

Answer 12

• 1894, found argon in atmosphere
• found helium (1895), neon (1898), krypton (1898) and xenon (1898)
• won noble peace prize in chemistry
• died due to radioactivity

Question 13

who is JJ Thompson

3

Answer 13

• discovered electrons (called them corpuscules)
• plum pudding model (- charge scattered around positive charge)
• started separating neon isotopes by mass leading to techniques of mass spectrometry

Question 14

who is marie curie

4

Answer 14

• investigated radioactive substances with pierre curie, husband
• discovered radium & polonium
• 2 nobel prizes (physics & chemistry)
• unit curie=radioactivity

Question 15

what is the plum pudding model

2

Answer 15

• by JJ thompson (early 1900s)
• atom is a + charged evenly distributed sphere/cloud w/ dispersed- charged e-

Question 16

what is the nuclear model of an atom

3

Answer 16

• by ernest rutherford thru his gold foil experiment
• discovered nucleus & proton
• also by james chadwick who found neutrons

Question 17

what is rutherford’s gold foil experiment

5

Answer 17

• if plum pudding, laser (+ charged, ALPHA) from gold foil should go straight bec. sphere is full of negative charges (attract)
• real result: some laser bounced from the gold foil and some went straight (bounced=repelled; straight=attract); concentrated + charge at center of atom=nucleus
• nucleus = positive charge and mass of the atom
• The rest of the atom is primarily empty space.
• tiny electrons surrounding + charged nucleus = neutral charge

Question 18

what are neutrons

Answer 18

neutral particles in nucleus & has similar mass with protons

Question 19

what is the electric charge & atomic charge of a proton

Answer 19

+1.602 x 10 -19 C
+1

Question 20

what is the electric charge & atomic charge of a neutron

Answer 20

0
0

Question 21

what is the electric charge & atomic charge of a electron

Answer 21

-1.602 x 10 -19
-1

Question 22

what is the mass and atomic mass of a proton

Answer 22

1.6726 x 10 -24
1.0073

Question 23

what is the mass and atomic mass of a neutron

Answer 23

1.6749 x 10 -24
1.0087

Question 24

what is the mass and atomic mass of an electron

Answer 24

9.1094 x 10 -28
0.00054858

Question 25

what is atomic no.

Answer 25

AXZ ∆ Z number of protons; atomic number; characteristic of element

Question 26

what is mass number

Answer 26

AXZ ∆ A protons + neutrons says isotopic nature

Question 27

what is a net charge

Answer 27

AXZ ∆ ^ #± ± = net charge protons-electrons

Question 28

what are ions

Answer 28

AXZ ∆ ^ #± charged particles when an atom loses or gains electrons

Question 29

what are anions

Answer 29

(-) charged ion (gain electron)

Question 30

what are cations

Answer 30

(+) charged ions (loss of electrons)

Question 31

what is an isotope | 3

Answer 31

* same element, same chem properties, different radioactive properties & weights * atoms have identical outsides but different insides (different neutrons) * by frederick soddy (noble prize in chemistry in 1913)

Question 32

how to get ave. atomic mass | 3

Answer 32

1. % to decimal 2. multiply to isotope atomic mass 3. get ave.

Question 33

what word did atom come from

Answer 33

atomos "indivisible" by democritus & leucippus

Question 34

what is bohr's model | think of solar system

Answer 34

* electrons moved around nucleus in orbits of fixed sizes and energies * quantisized electron energy (definite energy level per orbit; KLMN in to out; n=1,2,3,4, etc) * did not work for heavier atoms * postulated: only special orbits called discrete orbits of electrons are allowed inside atom & electrons do not radiate energy as they revolve (because normally, when an electron moves in a circular motion, it gains energy but it will collapse to the nucleus making it unstable)

Question 35

what is the brownian motion

Answer 35

when robert brown in 1827 placed pollen into water and looked at it thru a microscope and saw the pollens just jiggling = liquid atoms and pollens jiggle jiggle & einstein found the size of an atom