Atomic Theory - Study Guide PDF

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Atomic theory study guide...

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Atomic Theory ⊛ History ● Democritus (460 BC- 370 BC) ○

Named the most basic particle “atomos”.

○

Atomos - means indivisible and indestructible. ■

Not true: splitting atoms and subatomic particles was yet to be discovered.

● Aristotle ○

Didn’t believe in atoms, believed in continuous matter. ■

Believed everything was composed of air, fire, water, and earth.

● By 1700s, all chemists agreed… 1. on the existence of atoms. 2. that atoms combined to make compounds. ■

But still did not agree on whether elements combined in the same ratio when making a compounds.

● Antoine-Laurent Lavoisier ○

Introduced quantitative measurements to the laboratory.

○

Clarified the concept of an element as a substance that could not be broken down by any known method of.

● John Dalton (1766-1844) ○

DALTON’S ATOMIC THEORY 1. All mass is made of atoms.

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2. Atoms of the same element have the same size, mass, and properties. 3. Atoms can’t be subdivided, created or destroyed. 4. Atoms of different elements combine in whole number ratios to make compounds. 5. In chemical reactions, atoms are combined, separated, and rearranged. ● Discovery of the Electron ○

In 1897, J.J. Thomson used a cathode ray tube to deduce the presence of a negatively charged particle. ■

Cathode ray tubes pass electricity through a gas that is contained at a very low pressure.

○

Noted Qualities of Ray produced: ■

Existed: There was a shadow on the glass when an object was placed inside.

■

Had mass: The paddle wheel placed inside, moved from one end to the other so something must have been “pushing” it.

■

Negatively charged: The rays behaved the same way around a magnetic field as a conducting wire, were repelled by a negatively charged object.

● Thomson’s Atomic Model ○

Thomson believed that the electrons were like plums embedded in a positively charged “pudding”, thus it was called the “plum pudding” model.

● Robert Millikan (1868-1953)

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○

Oil Drop Experiment ■

Discovered the mass of an electron

● Rutherford’s Gold Foil Experiment ○

Particles were fired at a thin sheet of gold foil.

○

Particle hits on the detecting screen (film) are recorded.

● Discovery of Nucleus ○

Some particles (1/8000) bounced back from the foil.

○

This meant there had to be a “powerful force” to hit the particles back.

● Rutherford’s Findings ○

Most of the particles passed right through

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A few particles were deflected

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VERY few were greatly deflected

● Rutherford’s Conclusions ○

The nucleus is small.

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The nucleus is dense.

○

The nucleus is positively charged.

● Eumen Goodstein (1850-1930) ○

Discovered the proton

○

Also used the cathode ray tube and discovered the positively charged particles in an atom.

● James Chadwick (1891-1974) ○

Discovered the electron in 1932.

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● Law of Conservation of Mass ○

Mass is neither created or destroyed during regular chemical or physical changes.

● Law of Definite Proportions ○

Any amount of a compound contains the same element in the same proportions by mass.

● Law of Multiple Proportions ○

Applies when 2 or more elements combine to make more than one type of compound.

○

The mass ratios of the second element simplify to small whole numbers.

● Subatomic Particles ○

Number of protons identifies the atom as a certain element

○

Protons and neutrons are about same size

○

Electrons are much smaller

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Nuclear force: When particles in the nucleus get very close, they have a strong attraction. ■

Proton + Proton

■

Proton + Neutron

■

Neutron + Neutron

Particle

Charge

Mass Number

Location

Electron

-1

0

Electron Cloud

Proton

+1

1

Nucleus

Neutron

±0

1

Nucleus

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● Atomic Number ○

Atomic Number (Z) of an element is the number of protons in the nucleus of that element.

Element

# of Protons

Atomic # (Z)

Carbon

6

6

Phosphorous

15

15

Gold

79

79

● Mass Number ○

Mass Number: the number of protons and neutrons in the nucleus of an isotope.

○

Nuclide: A distinct kind of atom or nucleus characterized by a specific number of protons and neutrons.

Nuclide

p

n

e

Mass #

Oxygen

8

10

8

18

Arsenic

33

42

33

75

Phosphorous

15

16

15

31

● MASS # = Protons (p) + Neutrons (n) Modern Atomic Theory ● All matter is composed of atoms. ● Atoms cannot be subdivided, created, or destroyed in ordinary chemical reactions. However these changes CAN occur in nuclear reactions.

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● Atoms of an element have a characteristic average mass which is unique to that element. ● Atoms of any one element differ in properties from atoms of another element. Structure of Atom ● Nucleus ○

Contains protons and neutrons

○

Takes up very little space

● Electron Cloud ○

Contains electrons

○

Takes up most of the space of an atom

● Subatomic Particles ○

Includes all particles inside atom ■

Proton

■

Electron

Neutron Charge on protons and electrons are equal but opposite ■

○ ○

To make an atom neutral, need equal numbers of protons and electrons.

● Isotopes ○

Isotopes are atoms of the same element having different masses due to varying number of neutrons.

Isotope

Symbol

Composition of the Nucleus

% in nature

Carbon-12

12C

6 protons, 6 neutrons

98.89%

Carbon-13

13C

6 protons, 7 neutrons

1.11%

Carbon-14

14C

6 protons, 8 neutrons

sig figs -> 15.99, 16.00

● Compare and contrast mass number and atomic mass. ○

mass number = number of protons + number of neutrons (whole number), whereas atomic mass = average mass of an element, taking in consideration the abundance of the various isotopes

● What feature distinguishes a neutral atom from an ion? ○

Ions have different numbers of electrons compared to protons, whereas neutral atoms have equal numbers of protons and neutrons.

● If an ion has a -2 charge, what has been altered in the atom? ○

Gained 2 electrons

● If an ion has a +2 charge, what has been altered in the atom? ○

Lost 2 electrons

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Mass # Element Symbol Atomic # 40 K 19

18 F 9

31 S 16

Atomic #

19

9

16

29

26

35

Mass #

40

18

31

65

57

77

# of Protons

19

9

16

29

26

35

# of Electron s

19

9

16

27

23

36

# of Neutron s

21

9

15

36

31

42

Symbol

65 +2 57 +3 Cu Fe 29 26

77 -1 Br 35

● The Periodic Table: A helpful table which shows all the known elements in order of increasing atomic number. ● The Periodic Table ○

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Metals vs. Families ■

Most elements are metals and occur on the left side.

■

The nonmetals appear on the right side.

■

Metalloids are elements that have some metallic and some nonmetallic properties, “in between”

Groups/Families - elements in the same vertical columns; have similar chemical properties.

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Periods - horizontal rows of elements.

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● Atoms can form by gaining or losing electrons ○

Metals tend to lose one or more electrons to form positive ions called cations.

● Nonmetals tend to gain one or more electron to form negative ions called anions. ○

Named by using the root of the atom name followed by the suffix -ide.

● Ion Charges and the Periodic Table ○

The ion that a particular atom will form can be predicted from the periodic table.

Group or Family

Charge

Alkali Metals (1A)

1+

Alkaline Earth Metals (2A)

2+

Halogens (7A)

1-

Noble Gases (8A)

0

● Transition metals form cations with various charges. ● An ion with a 3+ charge contains 23 electrons. Which ion is it? a.

Fe3+

b.

V3+

c.

Ca3+

d.

Sc3+

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● A certain ion X+ contains 54 electrons and 78 neutrons. What is the mass number of this ion? ○

133...