How Big is an Atom?How Big is an Atom?

Imagine that you could increase the size Imagine that you could increase the size of an atom to make it as big as an of an atom to make it as big as an orange.orange.

How Big is an Atom?How Big is an Atom?

At this new scale, the orange would be as At this new scale, the orange would be as big as the Earth.big as the Earth.

What is an atom?What is an atom? Smallest unit Smallest unit

into which into which matter can be matter can be divided, while divided, while still maintaining still maintaining its properties.its properties.

An Element is An Element is composed of composed of ONE type of ONE type of atom.atom.

Aim: The scientific study of the Aim: The scientific study of the atom began with John Dalton in atom began with John Dalton in the early 1800’s and has been the early 1800’s and has been

revised through the years.revised through the years.The atomic Model of MatterThe atomic Model of Matter

John Dalton (1803-1807)John Dalton (1803-1807)

J.J. Thomson (1897)J.J. Thomson (1897)

Ernest Rutherford (1910)Ernest Rutherford (1910)Niels Bohr (1913)Niels Bohr (1913)

Wave-Mechanical ModelWave-Mechanical Model

The Dalton Model 1803The Dalton Model 18031) Each element is composed of indivisible 1) Each element is composed of indivisible

atoms.atoms.

2) In an element, all the atoms are identical; 2) In an element, all the atoms are identical; atoms of different elements have different atoms of different elements have different properties, including mass.properties, including mass.

3) In a chemical reaction, atoms are not created, 3) In a chemical reaction, atoms are not created, destroyed, or changed into other types of destroyed, or changed into other types of atoms.atoms.

4) Compounds are formed when atoms of more 4) Compounds are formed when atoms of more than one element combine.than one element combine.

5) Dalton’s model = solid, indivisible, sphere. 5) Dalton’s model = solid, indivisible, sphere.

DOES NOT mention subatomic particlesDOES NOT mention subatomic particles

Solid Sphere No Charged Particles

J.J. Thomson 1897J.J. Thomson 18971.1. Examined cathode rays (electric charge Examined cathode rays (electric charge

that flows from the negative electrode, that flows from the negative electrode, (cathode) to a positively charged electrode, (cathode) to a positively charged electrode, (anode).(anode).

2.2. These cathode rays were the paths of These cathode rays were the paths of negatively charged particles he called negatively charged particles he called electrons. electrons.

Cathode Ray Tube - YouTubeCathode Ray Tube - YouTube

PLUM PUDDING model: PLUM PUDDING model:

Positively charged sphere with electrons Positively charged sphere with electrons embedded in it like raisins in plum embedded in it like raisins in plum pudding. He gave the atom some structure. pudding. He gave the atom some structure.

Plum Pudding ModelPlum Pudding Model

What happens when you What happens when you bite into a peach?bite into a peach?

The Rutherford Model The Rutherford Model 19111911Bombarded thin gold foil with the radioactive Bombarded thin gold foil with the radioactive

nuclei of Helium atoms (+ charged alpha nuclei of Helium atoms (+ charged alpha particles) and observed how these particles particles) and observed how these particles were scattered by the foils. were scattered by the foils.

1 in 20,000 particles bounced back or were 1 in 20,000 particles bounced back or were deflected, the rest past through the gold deflected, the rest past through the gold sheets. sheets. Rutherford's Model of the Atom - YouTubeRutherford's Model of the Atom - YouTube

ConclusionConclusion1) Most of the atom is empty space with a 1) Most of the atom is empty space with a

dense (+) charged nucleus.dense (+) charged nucleus.2) The atom has a dense (+) nucleus.2) The atom has a dense (+) nucleus.3) The electrons are present and orbit the 3) The electrons are present and orbit the

space surrounding the nucleus. space surrounding the nucleus.

Rutherford ExperimentRutherford Experiment

Neils Bohr 1913Neils Bohr 1913The Bohr Model – electrons travel in fixed The Bohr Model – electrons travel in fixed

circular pathways or ORBITALS around circular pathways or ORBITALS around the nucleus, held in place by the the nucleus, held in place by the proton(s) in the nucleus. proton(s) in the nucleus.

Why we see LightWhy we see Light

1) Electrons absorb energy and jump to 1) Electrons absorb energy and jump to higher orbitals. The electron gives off higher orbitals. The electron gives off the excess energy as light and falls back the excess energy as light and falls back down to lower energy levels.down to lower energy levels.

2) Light given off by the atoms corresponds 2) Light given off by the atoms corresponds to certain frequencies or energies.to certain frequencies or energies.

Wave Mechanical ModelWave Mechanical ModelShows the area with the greatest probability

of finding an electron(s)

Bohr Model vs. Wave Mechanical ModelBohr Model vs. Wave Mechanical Model

Bohr ModelBohr ModelBohr's model gives

the electron orbit an exact travel path.

Wave Wave MechanicalMechanical

1.1. The electron(s) make The electron(s) make an orbital cloud of the an orbital cloud of the most probable location most probable location around the nucleus.around the nucleus.

Bright Line SpectraBright Line Spectra

Structure of an AtomStructure of an Atom

Made up of the Made up of the subatomic particles: subatomic particles: Protons Protons

(positive)(positive) Neutrons (neutral)Neutrons (neutral) ElectronsElectrons

(negative)(negative)

+

-++

+

-

-

- -+

Energy Levels or Orbitals

The Atom’s “CENTER” Protons and neutrons are grouped together to

form the “center” or nucleus of an atom.

-

+++

Notice that the electrons are not apart of the nucleus. They are found in the electron cloud.

--

Subatomic Particle Weight Subatomic Particle Weight

ComparisonComparison Expressed in Expressed in AAtomic tomic MMass ass UUnits (AMU)nits (AMU)

+

-+

----- - -

--

---

--

--

-

- ----- - -

--

---

--

--

-

1836 electrons = 1 proton1839 electrons = 1 neutron

How do you think the mass of a neutron compares to that of a proton?

1 neutron ≈ 1 proton

Atoms are Electrically Atoms are Electrically NeutralNeutral

8 protons

8 electrons

+ =

Number of Protons = Number of

Electrons

No Charge++++

+++ + - - - -

- - - -

Sub-atomicParticle

Symbol Location Electric Charge

MassAtomic mass unit

(AMU)

Electron e- Outside the

nucleus

1- 1/1840

Proton p nucleus 1+ 1 amu

Neutron n nucleus 0 1 amu

Atomic NumberAtomic Number

NeutronsNeutrons1) Neutrons add mass to an atom, but they do not 1) Neutrons add mass to an atom, but they do not

change the atom’s identity as an element. change the atom’s identity as an element.

2) Neutrons are located inside the nucleus with 2) Neutrons are located inside the nucleus with the protons.the protons.

# of neutrons + # of protons = MASS NUMBER# of neutrons + # of protons = MASS NUMBER

Mass number – Atomic number = # of neutronsMass number – Atomic number = # of neutrons

3) All atoms on the periodic table are electrically 3) All atoms on the periodic table are electrically neutral.neutral.

Give the symbol, atomic number, # of protons, Give the symbol, atomic number, # of protons, neutrons, and electrons, and atomic mass for neutrons, and electrons, and atomic mass for Argon. Argon.

Isotopic SymbolsIsotopic Symbols

Isotope Notation – Concept Isotope Notation – Concept CheckCheck

1.1. Atomic Number = Atomic Number = 2.2. Atomic Mass = Atomic Mass = 3.3. Protons =Protons =4.4. Electrons = Electrons = 5.5. Neutrons =Neutrons =

Mass NumberMass Number The total number of protons and neutrons in the The total number of protons and neutrons in the

nucleusnucleus

What is the mass number of this atom?

3 4

5 protons + 6 neutrons = a mass number of

11 amu+++

--

-

++

-

-

What is the overall charge of this atom?

Bohr Model vs. Wave Bohr Model vs. Wave Mechanical Model Mechanical Model Niels Bohr s Atomic Model - Niels Bohr s Atomic Model -

YouTubeYouTube

1.1. Niels Bohr based his atomic Niels Bohr based his atomic model on his observations using model on his observations using HydrogenHydrogen… …

2.2. Hydrogen has only 1 electron.Hydrogen has only 1 electron.

Bohr Diagrams

1) Find your element on the periodic table.

2) Determine the number of protons and neutrons in the atom. How can we do this?

3) Atomic Number = Proton number.

4) Mass Number – Atomic Number = Neutron #

Bohr Diagrams

CC

1) Draw a nucleus with the number of protons and neutrons.

2) Carbon has two energy levels, or shells. (electron configuration)

3) Draw the shells around the nucleus.

Bohr Diagrams

1) Add the electrons.2) Carbon has 6 electrons.3) The first shell can only

hold 2 electrons.4) The second shell will

contain the other 4 electrons.

CC

Bohr DiagramsBuild a Bohr Diagram

1) Check your work.

2) You should have 6 total electrons for Carbon.

3) How many total electrons can fit in the third shell?

CC

8

Absorption and Release of Energy by an Absorption and Release of Energy by an electronelectron

1) When an electron absorbs a specific amount of energy (known as quanta or quantum of energy), the electron becomes excited and moves or “jumps” to a higher energy orbital.

2) When the electron “jumps” to a higher energy level or orbital it is said to be in the excited state.

3) When the electron releases this excess energy, it releases

the energy as a photon of light and falls to the ground state.

4) The color light that is emitted or released is determined by how many orbitals and which orbitals the electron “falls” back.

OrbitalsAtomic Emission Animation - YouTube

n=3 -----------------------------------------------------

n=2 ----------------------------------------------------

n=1 ----------------------------------------------------

Neils Bohr 1913Neils Bohr 1913Bohr - YouTubeBohr - YouTube

Bohr Model vs. Wave Bohr Model vs. Wave Mechanical ModelMechanical Model

Quantum Mechanics: The Structure Of Atoms - YouTubeQuantum Mechanics: The Structure Of Atoms - YouTube

Bohr ModelBohr ModelWhen a Hydrogen eWhen a Hydrogen e––

was excited, the was excited, the light emitted was light emitted was

found to be found to be composed of composed of

regularly spaced regularly spaced lines. Each element lines. Each element

has ahas a

Visible-line Visible-line spectrum.spectrum.

Wave MechanicalWave MechanicalAn atomic orbital is the An atomic orbital is the

region of space region of space around the nucleus around the nucleus where the probability where the probability of locating an eof locating an e–– with with a given energy is a given energy is greatest.greatest.

The bright-line spectra for three elements and a mixture of elements are shown below.

1) Identify all the elements in the mixture. 2) Explain, in terms of both electrons and energy, how the bright-line spectrum

of an element is produced.3) State the total number of valence electrons in a cadmium atom in the ground

state.

Ground State vs. Excited StateGround State vs. Excited State

1) 1) Ground StateGround State – all electrons are – all electrons are in the lowest possible energy in the lowest possible energy

levels (normal) levels (normal) ex.ex. 2 – 7 2 – 7

2) 2) Excited StateExcited State – if given – if given additional energy, electrons will additional energy, electrons will

“jump up” to higher energy “jump up” to higher energy levels, temporarily.levels, temporarily.

Excited State Excited State ex.ex. 2 – 5 – 2 2 – 5 – 2 Ground State Ground State ex.ex. 2 – 7 2 – 7

Bright Line Emission SpectraBright Line Emission SpectraHow does this happen?How does this happen?

1.1. ““Excited electrons” at higher energy Excited electrons” at higher energy levels will eventually release the extra levels will eventually release the extra energy and “fall back down” to energy and “fall back down” to ground state conditions. ground state conditions.

2.2. During the “fall back”, energy is During the “fall back”, energy is

released as Visible Light Energy.released as Visible Light Energy.

Bright Line – Emission Bright Line – Emission SpectraSpectra

What evidence indicates that What evidence indicates that electrons move around the electrons move around the nucleus in definite pathways?nucleus in definite pathways?

How would you compare How would you compare different element’s different element’s

spectral line patterns to spectral line patterns to an individual’s DNA?an individual’s DNA?

Unknown DNA SampleUnknown DNA Sample MatchMatch

1) Each element has a specific 1) Each element has a specific electron configuration and a electron configuration and a corresponding corresponding emission spectrumemission spectrum..

2) Emission (bright line) spectrum 2) Emission (bright line) spectrum can be used to identify can be used to identify (“fingerprint”) each element.(“fingerprint”) each element.

Use your Sun block to block UVA and UVB rays!Use your Sun block to block UVA and UVB rays!

Lewis Structures of Atoms1) The chemical symbol for the atom is surrounded

by a number of dots corresponding to the number of valence electrons.

2) Valence electron(s) – number of electrons in the atom’s outermost orbital. These are the electrons involved in chemical bonding between atoms.

3) Kernel – Nucleus (protons and neutrons) and all non-valence electrons.

Lewis and Bohr

Lewis StructuresLewis StructuresIn your notes, try In your notes, try these elements on your these elements on your own:own:

a)a) HH

b)b) PP

c)c) CaCa

d)d) ArAr

e)e) ClCl

f)f) AlAl

Lewis Structures of Lewis Structures of atoms and ionsatoms and ions

Sodium (Na) –Sodium (Na) – Yellow flameYellow flamewith Na salts with Na salts

like NaCl, like NaCl, NaBrNaBr

Potassium (K) –Potassium (K) –

Violet flameViolet flamewith KCl, KBr, with KCl, KBr,

etc.etc.

Isotopes of an element account Isotopes of an element account for the average atomic massfor the average atomic mass

Isotopes- Atoms of the same element Isotopes- Atoms of the same element can have the same number of can have the same number of protons, BUT different numbers of protons, BUT different numbers of neutrons. neutrons.

Atoms with a few too many neutrons, Atoms with a few too many neutrons, or not quite enough, can sometimes or not quite enough, can sometimes exist for a while, but they're exist for a while, but they're unstable. unstable.

How can we calculate the How can we calculate the Average Atomic Mass for an Average Atomic Mass for an

atom?atom?Atomic mass or atomic weight Atomic mass or atomic weight - the average mass - the average mass

of atoms of an element, calculated using the of atoms of an element, calculated using the relative abundance of relative abundance of naturally-occurring naturally-occurring isotopes of an element. isotopes of an element.

RememberRemember

The mass on the periodic table is the average of all The mass on the periodic table is the average of all the naturally occurring isotopes of that element.the naturally occurring isotopes of that element.

C = 12.011C = 12.011

238U with an abundance of 99.28%

235U has an abundance

of 0.72%

Carbon’s Naturally Occurring Carbon’s Naturally Occurring IsotopesIsotopes

Carbon Carbon Naturally Occurring Naturally Occurring

IsotopesIsotopes98.89% of C atoms are 12C

1.108% of C atoms are 13C

Σ (mass of isotope × relative Σ (mass of isotope × relative abundance)abundance)

Average mass of C with 98.89% C-12 Average mass of C with 98.89% C-12 and and

1.108% C-131.108% C-13

******Remember to divide the percentages by Remember to divide the percentages by 100100

98.89%/100% = .988998.89%/100% = .9889

1.108%/100% = .011081.108%/100% = .01108

MMavgavg= [(.9889)(12) + (.01108)(13)]= [(.9889)(12) + (.01108)(13)]

MMavgavg = [(11.8668) + (0.14404)] = [(11.8668) + (0.14404)]

MMavgavg = 12.011 amu = 12.011 amu

Chemistry: Average Atomic MassChemistry: Average Atomic Mass

IonsIons

Ions:Ions: neutral atoms that have either gained or neutral atoms that have either gained or lost electron(s). Number of protons and neutrons lost electron(s). Number of protons and neutrons remains the same.remains the same.

Cation: atom loses 1 or more electrons to become a Positively charged ion.

Anion: atom gains 1 or more electrons to become a Negatively charged ion.

Which has a larger atomic radius, Which has a larger atomic radius, the neutral atom or the ion? Explainthe neutral atom or the ion? Explain.