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Atomic Structure

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Defining the Atom

Atom – smallest particle of an

___________ that retains the

chemical __________ of that

element

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Defining the Atom

The Greek philosopher Democritus (460

B.C. – 370 B.C.) was among the ______

to suggest the existence of ________ (from the Greek word “atomos”)‏

He believed that atoms were indivisible and

indestructible

His ideas did agree with later scientific

theory, but did not explain chemical

behavior, and was not based on the

scientific method – but just _____________ 4

Dalton’s Atomic Theory (experiment based!)‏

1) Atoms of different elements combine in

simple whole-number ratios to form

chemical _____________

2) In chemical reactions, atoms are combined,

separated, or rearranged – but __________

changed into atoms of another element.

1) All elements are composed of

tiny indivisible particles called

__________

2) Atoms of the same element are

__________. Atoms of any one

element are ___________ from

those of any other element.

John Dalton

(1766 – 1844)

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Sizing up the Atom Elements are able to be subdivided into

smaller and smaller particles – these are

the ___________, and they still have

___________ of that element

If you could line up 100,000,000

copper atoms in a single file, they

would be approximately 1 cm long

Despite their small size, individual

atoms are observable with instruments

such as scanning tunneling (electron)

microscopes 6

Structure of the Atom

One change to Dalton’s atomic theory is that atoms are ___________ into subatomic particles:

____________, _________, and ____________ are examples of these fundamental particles

There are many other types of particles, but we will study these three

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Thomson’s Atomic Model

Thomson believed that the electrons

were like plums embedded in a

_________ charged “pudding,” thus it

was called the “____ pudding” model.

J. J. Thomson

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Although Thompson had the

positive and negative particles in

the wrong place, he is credited

with discovering ___________.

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Earnest Rutherford’s

Experiments

a) The nucleus is _______

b) The nucleus is _______

c) The nucleus is __________

charged

Conclusions:

This “fixed” Thompson’s plum

pudding model. Rutherford is

credited with discovering the

______________. 10

The Rutherford Atomic Model Based on his experimental evidence:

The atom is mostly _________ space

All the positive charge, and almost all the

_______ is concentrated in a small area in

the ________. He called this a “nucleus”

The nucleus is composed of _______ and ___________ (they make the nucleus!)‏

The ____________ distributed around the

nucleus, and occupy most of the _________

His model was called a “nuclear model”

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Bohr Model

Neils Bohr discovered _______ _______

of electrons. He said that electrons

orbited the nucleus like planets orbit the

___…he was wrong about the orbiting but

right that there are particular energy levels

that electrons reside in.

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Modern (Wave) Model of the Atom

The modern model of the atom consists of

__________ that electrons move around

in…we will discuss later.

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About Atoms

There are presently ___ elements, thus 118 _________ kinds of ________.

These atoms _________ in many different combinations and proportions to form the tremendous number of ___________ found.

Experiments determined that atoms contain three ______________ particles: protons, neutrons, and electrons.

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Atoms have a positively charged dense central core called a nucleus. The nucleus contains protons and neutrons.

Protons – __________ charge

Neutrons – _________ or zero charge

Protons and neutrons have about the same mass.

Electrons move in the space around the nucleus called the _______________.

Electrons – _________ charge

Electron’s mass is _____ _____ ____ than that of neutrons and protons.

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The nucleus is much more __________

but much ___________ than the electron

cloud. If you made a model of an atom to

scale – use __________ as nucleus, the

end of the atom would be 2 ___________

fields away from the baseball.

abbreviations commonly used: p+, no, e-

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Subatomic Particles

1.675 x 10-24 g

__ amu

Neutron

(no)

1.673 x 10-24 g

__ amu

Proton

(p+)

9.11 x 10-28 g

Approx. _ amu

Electron

(e-)

Location Mass (g) and

Mass (amu)

Charge Particle

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Atomic Number – tells the number of _______ in an atom. It is found on the periodic table.

Ex: there are __ protons in an atom of Nitrogen, there are ___ protons in an atom of Uranium

The number of ________ in an atom makes the atom what it is! Ex. Potassium has 19 protons it can never have any more or any less and still be potassium.

Individual atoms are electrically _________, which means they have the _____ number of ________ as __________. Ex. An atom of copper has ___ protons and ___ electrons.

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Mass Number – ____ of _______ and

___________ of a particular atom.

Ex. “Chlorine-37” Ex. “Aluminum-27”

Atomic number: Atomic number:

Mass number: Mass number:

p+: p+:

e-: e-:

no: no:

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Naming Isotopes

The number written after an

element name is always the

______ number for a particular

isotope of that atom.

carbon-12

carbon-14

uranium-235 20

Mass Number

Mass number is the number of

protons and neutrons in the nucleus

of an isotope: Mass # = p+ + n0

- 31

-

Oxygen -

Mass # e- n0 p+ Nuclide

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Arsenic 75

Phosphorus

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Question: Why do you think the “mass” number only includes protons and neutrons?

Answer: because protons and neutrons both have a mass of __ amu, but electrons have a mass of __ amu

Question: Why do you think the mass number is always a whole number?

Answer: because there are always ________ numbers of protons and neutrons in an atom

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Complete Symbols

Contain the symbol of the element,

the mass number and the atomic

number.

X Mass

number

Atomic

number Subscript →

Superscript →

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Symbols

Find each of these:

– number of protons

– number of

neutrons

– number of

electrons

– Atomic number

– Mass Number

Br 80

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Symbols

If an element has an atomic

number of 34 and a mass

number of 78, what is the:

– number of protons

– number of neutrons

– number of electrons

– complete symbol

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Symbols

If an element has 91

protons and 140 neutrons

what is the

– Atomic number

– Mass number

– number of electrons

– complete symbol 26

Symbols

If an element has 78

electrons and 117 neutrons

what is the

– Atomic number

– Mass number

– number of protons

– complete symbol

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Isotopes

Dalton was wrong about all elements of the same type being _____________

Atoms of the same element can have ___________ numbers of __________.

Thus, different _________ numbers.

These are called isotopes – atoms with the same number of protons but different number of neutrons...thus they have different masses.

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Isotopes

Elements occur in _________ as

____________ of isotopes.

Ex. Chlorine exists as chlorine-__ and

chlorine-__. Both have __ protons

but one has __ neutrons and one has

__ neutrons.

•There is no way of predicting which

isotopes exist for each element; these

have been _______________ determined.

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Atomic Mass How heavy is an atom of oxygen?

It depends, because there are different ________ of oxygen atoms.

We are more concerned with the average atomic mass. (this number is found on the ‏(______ _________

This is based on the _____________ (percentage) of each variety of that element in _________.

We don’t use ________ for this mass because the numbers would be too small.

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Measuring Atomic Mass

Instead of grams, the unit we use is the Atomic Mass Unit (_____)‏

Each isotope has its own atomic mass, thus we determine the average from percent abundance, which is why it is a ___________ and not a _________ number.

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Atomic Masses

<0.01% 6 protons

8 neutrons

14C Carbon-14

1.11% 6 protons

7 neutrons

13C Carbon-13

98.89% 6 protons

6 neutrons

12C Carbon-12

% in nature Composition of

the nucleus

Symbol Isotope

Atomic mass is the average of all the

naturally occurring isotopes of that element.

Carbon = 12.011 32

To get the “most __________

mass number”, __________ the

atomic mass off to the nearest

whole number.

Example: What is the most

common mass number of the

following? Ag, Cu, C, Cl

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Draw models of lithium-5, lithium-6, and

lithium-7 atoms including the correct

numbers of protons, neutrons, and

electrons in each.

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IONS

Ion – atom that has _______ or ____ electrons

Two types:

_________ – a positive ion, one that has

_______ electrons

_________ – a negative ion, one that has

_________ electrons

Atoms NEVER gain or lose __________ or

____________ (except in nuclear reactions)‏

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Examples

Mg is a magnesium atom and has ___ protons

and ___ electrons so the overall charge is ____.

Mg+2 is a magnesium ion and has ___ protons

and ___ electrons so the overall charge is ____.

Cl is a chlorine atom and has ___ protons and

___ electrons so the overall charge is ____.

Cl- is a chlorine ion has ____ protons and

___ electrons so the overall charge is ____.

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Examples:

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Energy Levels

Who was the first to notice that the electron cloud

has different regions where electrons reside?

There are various ______________ in an electron

cloud. Within each energy level there are

_____________ and within each sublevel there are

__________. Each orbital can hold up to two

electrons.

Electrons move very ________ within their own

______________.

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Maximum number of electrons

Energy levels (n) can

hold a maximum number

of 2n2 electrons.

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6

5

4

3

2

1

Max num

of e-

Energy

level

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More about energy levels…

The total number of __________ levels an atom has corresponds to the _________ number of the atom.

Periods are the ______________ rows on the PT

Ex. An atom of bromine has ___ energy levels because it is in period ___

The ______ energy level, called the ____________ shell, can hold ONLY up to ______ electrons.

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Valence Electrons

_____________ electrons are the electrons in

the __________ energy level.

The atoms are arranged on the periodic table so

that the ones with ___________ properties all

line up in a ____________ or __________.

The ____________ of valence electrons plays a

big role in how the atom _____________.

41 Except He (2) 18 (8A)

17 (7A)

16 (6A)

15 (5A)

14 (4A)

13 (3A)

3-12 and the actinides and

lanthanides (B’s)

2 (2A)

1 (1A)

Number of Valence e- Group Number

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Electron dot diagrams

Use the number of valence electrons as _______

and space them around the ________ sides of

the element’s symbol then ________ up as

needed

Examples:

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Group/Family Names to Label

Alkali Metals

Alkaline Earth Metals

Transition Metals

Lanthanides

Actinides

Boron Family

Carbon Family

Nitrogen Family

Oxygen Family

Halogens

Noble Gases

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Periods

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Ion Charge Prediction

Octet rule – atoms will ________, _________ or share electrons so that they have a ______________ ________________ shell

That's ____ electrons for everything except 1st shell (H and He) which only holds __ electrons

Ex. Nitrogen has ___ valence electrons so it will gain ___ to make ___. N-3

Ex. Sodium has___ valence electron so it will lose that one and the _________ shell becomes the valence shell with ___ electrons. Na+

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Group 1 (1A) makes ____

Group 2 (2A) makes ____

Group 3-12 (B's) are __________________

Group 13 (3A) makes ____

Group 14 (4A) makes ____

Group 15 (5A) makes ____

Group 16 (6A) makes ____

Group 17 (7A) makes ____

Group 18 (8A) makes ____ (doesn't form ions!) why?

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Examples:

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Electron Configurations

AUFBAU principle – electrons fill orbitals starting with the _____________ energy orbital available before filling higher energy orbitals.

PAULI EXCLUSION principle – each orbital can hold at most _ electrons and they must have _______ spins (clockwise and couterclockwise)‏

HUND'S rule – electrons occupy equal-energy orbitals so that a maximum number of _______ electrons results ex. __ __ __ not __ __ __ **spread out before pairing up**

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Sublevels: s, p, d and f

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Orbitals

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Writing electron configurations

Use the periodic table as a guide.

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More Electron Configurations

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Abbreviated Electron Configurations

Use the previous _______________ to shorten the electron configuration.

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Orbital Notation

Use ________ to represent electrons.

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Exceptions to Orbital Fill Order

Any electron configuration that ends in ____ is too ___________ and actually takes an electron from the previous ___ sublevel and becomes ____.

Example:

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Another Exception

Any electron configuration that ends in ____ is too ___________ and actually takes an electron from the previous __ sublevel and becomes _____.

Example:

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Examples:

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Absorption and Emission

Normally, electrons in an atom are in the ____________ state, which means they are in the _______________ possible energy levels.

However, these electrons can be ___________ to higher energy levels if energy is added...called _________________.

If energy is absorbed and the electrons jump to higher energy levels they are now in the ________________ state.

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Once in the excited state the atoms are ______________ and thus _______ energy when they fall back down to their original energy levels. This process is called _______________.

This __________ of absorption and emission happens very fast over and over again.

Atoms can be excited using _________, light, or electricity.

Emission is usually in the form of __________. Different energies of light have different ___________. The light spectrum: (lower energy)ROYGBIV (higher energy)‏

This is actually how we see colors!

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