2 atomic structure b kartic

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Houston Community College System Chemistry 1405

Chapter 2Chapter 2

Atomic StructureAtomic Structure

By

Mounia Elamrani

Blei / Odians General, Organic, and Biochemistry


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Mounia Elamrani Chapter 2 The Atomic Structure

ObjectivesObjectives

Percent composition

Daltons atomic Theory

Constant composition of matter andconservation of mass

Atomic mass Atomic structure

Periodic table and properties of elements

Electron configuration and the valence shells Octet rule


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The early atomic theory 2.1The early atomic theory 2.1

The concept of the atom had limited scientificusefulness until the discovery of twoimportant laws in 18th and 19th centuries: The Law of conservation of mass: No detectable

gain or loss of mass occurs in chemical reactions.

Mass is conserved.

The Law of constant composition: In a givenchemical compound, the elements are always

combined in the same proportions by mass.


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Percent composition 2.1Percent composition 2.1

The usual form for describing the relativemasses of the elements in a compound is alist of percentages by mass, called thepercent composition

It is the number of grams of the element in100 g of the compound and can be calculatedusing:

100%element%samplewholeofmass

elementofmass=


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ExampleExample

Analysis of 4.800g of niacin, one of the B-complex vitamins, yields 2.810g of C, 0.1954gof H, 0.5462g of N, and 1.249g of O. Calculatethe mass percent of each element in thecompound.

%26.02100%O%

%11.38100%N%

%4.071100%H%

%58.54100%C%

sampleg0.5462

Og1.249

sampleg4.800

Ng0.5462

sampleg4.800

Hg0.1954

sampleg4.800Cg2.810

==

==

==

==


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Dalton 2.2Dalton 2.2s Atomic Theorys Atomic Theory

Matter consists of tiny particles called atoms.

In chemical reactions, the atoms rearrange butthey do not themselves break apart.

In any sample of a pure element, all the atomsare identical in mass and other properties.

The atoms of different elements differ in massand other properties.

In a given compound the constituent atoms arealways present in the same fixed numerical ratio.


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Atomic Mass 2.3Atomic Mass 2.3

It follows from Daltons Atomic Theory thatatoms of an element have a constant,characteristic atomic mass or atomicweight

For example, for any sample of hydrogenfluoride: F-to-H atom ratio: 1 to 1

F-to-H mass ratio: 19.0 to 1.00 This is only possible if each fluorine atom is

19.0 times heavier than each hydrogen atom


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)Atomic Mass Units )amu, u 2.3)Atomic Mass Units )amu, u 2.3

Atoms have extremely small masses. Themass of the heaviest known atom is about 4 x10-22 g.

We define the atomic mass unit, amu, usingCarbon-12 as the standard: 1 atom of carbon-12 = 12 u (exactly) 1 u = 1/12 of mass of 1 atom of carbon-12 (exactly)

This definition results in the assignment ofapproximately 1 u for the mass of hydrogen(the lightest atom)


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The structure of atoms 2.4The structure of atoms 2.4

Experiments have been performed that showatoms are comprised of subatomic particles

There are three principal kinds of subatomicparticles:

Proton )p carries a positivecharge, found in thenucleus, mass1u

Electron )e carries a negativecharge, foundoutside the nucleus, about 1/1800 the mass of a

proton, mass0u

Neutron )n carries no charge, found in thenucleus, a bit heavier than a proton, mass1u


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Atomic number and mass 2.4Atomic number and mass 2.4

numbernumber The number of protons in the nucleus is called

the atomic number(Z), and is unique foreach element.

Z = number of protons

The mass number(A) of an atom is the totalnumber of particles in the nucleus:

A = (number of protons) + (number of

neutrons)

The charge is given by:

Charge = number of proton - number ofelectrons


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ExercisesExercises

What is the charge of an atom containing 9p,10n, and 9e?

What is the charge of an ion containing 12p,

13n, and 14e?

Which element has 22p and 26n, and what isits approximate mass?


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Isotopes 2.5Isotopes 2.5

It turns out that most elements in nature areuniform mixtures of two or more kinds ofatoms with slightly different masses

Atoms of the same element with differentmasses are called isotopes

Isotopes have the same atomic number (Z)

but different mass (A)


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Counting Particles in Isotopes 2.5Counting Particles in Isotopes 2.5

Naturally occurring carbon consists of threeisotopes, 12C, 13C, and 14C. State thenumber of protons, neutrons, and electrons ineach of these carbon atoms.

12C 13C 14C6 6 6

#P _______ _______ _______

#N _______ _______ _______#E _______ _______ _______


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Calculating an element 2.5Calculating an element 2.5s averages average

atomic massatomic mass We average the masses of isotopes using

their masses and relative abundances to givethe average atomic mass of an element:

Naturally occurring chlorine is a mixture of

two isotopes:

ContributionMass(u)

Abundance(%)

Isotope

0.7577 * 34.9689 =26.50 u

34.968975.77Cl-35

0.2423 * 36.9659 =8.957 u

36.965924.23Cl-37

(Rounded) Total =35.46 u


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The Periodic Table 2.6The Periodic Table 2.6

It Arranges elements by increasing atomicnumber

Elements are arranged in numbered rowscalled periods

The vertical columns are called groups orfamilies (group labels vary)

Elements with similar physical and chemicalproperties, are placed in vertical columns, or

groups.Li, Na, K: are soft, very reactive metals.

He, Ne, Ar:are non reactive gases.


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2.6 Some important classifications2.6 Some important classifications

A groups = representative elements or maingroup elements I A= alkali metals II A = alkaline earth metals VI A = chalcogens VII A = halogens VIII = noble gases

B groups = transition elements Inner transition elements = elements 58-71

and 90-103 58 71 = lanthanide elements 90 103 = actinide elements


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Modern Periodic Table 2.6Modern Periodic Table 2.6

Note: Placement of elements 58 71 and 90 103 saves space


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Metals, Nonmetals, and 2.6Metals, Nonmetals, and 2.6

MetalloidsMetalloids Metals

Tend to shine (have metallic luster)

Can be hammered or rolled into thin sheets(malleable) and can be drawn into wire (ductile)

Are solids at room temperature (except Hg) and

conduct electricity


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Metals, Nonmetals, and 2.6Metals, Nonmetals, and 2.6

MetalloidsMetalloids Nonmetals

Lack the properties ofmetals

At room T can be solid,liquid, or gas

React with metals toform (ionic) compounds

Metalloids Have properties between

metals and nonmetals(semiconductors)


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2.6 Metals, Nonmetals, and2.6 Metals, Nonmetals, and

MetalloidsMetalloids


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Electron Organization Within 2.7Electron Organization Within 2.7

The AtomThe Atom Some early scientists thought that electrons

were orbiting around the nucleus

Later scientist discovered, through theemission of light by the elements, that

electrons have energy states It all started with atomic emission spectra...


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Continuous SpectrumContinuous Spectrum vs.vs. LineLine

SpectrumSpectrum

Hydrogen Line Spectrum

Na KRb

Visible Light Spectrum


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Electromagnetic Radiation and 2.7Electromagnetic Radiation and 2.7

EnergyEnergy Radiation carries energy through space

Light is a form ofelectromagneticradiation

Electromagnetic radiation is characterized by

its wave nature The frequency , (in Hz or s-1), of a radiation

is the number ofwaves, or completevibrations, in one second

Each color of the rainbow has a specificfrequency

Visible light range: 8x104 to 4x104 Hz

The higher the energy of the radiation, the


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Electromagnetic Radiation and 2.7Electromagnetic Radiation and 2.7

EnergyEnergy


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Atomic Energy States 2.7Atomic Energy States 2.7

Plancksaid that energy

can only be absorbed orreleased from atoms infixed amounts calledquanta

Atoms absorb energyfirst, then they release itin the form of a radiation(or color if in the visiblerange)

When energy isabsorbed, the e- jumpsto the excited state

When energy isreleased, or emitted, thee- drops to the ground

Excited State

Ground State

Absorption Emission


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The Quantum Mechanical Atom 2.8The Quantum Mechanical Atom 2.8

Complex mathematical theory that was ableto predict a variety of atomic properties

The detailed structure of the atom canexplain the periodicity of the chemical

properties of elements Elements can be built by adding electrons

and protons to the nuclei

There are rules guiding the way the electrons

are organized


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Bohr Model 2.8Bohr Model 2.8

First model of the electronstructure

Gives levels where anelectron is most likely to be

found Incorrect today, but a key

in understanding the atom


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Shells, Subshells, and OrbitalsShells, Subshells, and Orbitals

Shells Contain electrons that are similar inenergy and distance from nucleus: Low energy electrons are closest to the nucleus

Identified by a whole number (1, 2, 3) called theprincipal quantum number (n)..

The first shell (n=1) is lowest in energy, the 2ndlevel is next in energy (n=2) and so on: 1


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Number of ElectronsNumber of Electrons

Maximum number of electrons in any level =2n2

n =1 2(1)2 = 2n =2 2(2)2 = 8

n =3 2(3)2 = 18


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Order of Electron FillingOrder of Electron Filling

All electrons in the same energy level havesimilar energy.

Shell 1 2 electrons

Shell 2 8 electrons

Shell 3 18 electrons (8 first,later 10)

Order of filling for the first 20 electrons

Shell 1 2 3 4

2e 8e 8e 2e


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Electron ConfigurationElectron Configuration

Lists the shells containing electrons

Written in order of increasing energy

Element \ Shell 1 2 3

He 2

C 2 4F 2 7

Ne 2 8

Al 2 8 3Cl 2 8 7


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ExercisesExercises

A. The electron configuration for sulfur

1) 2,6 2) 8,2,6 3) 2, 8, 6

B. The element in period 3 with two electrons

in the outermost energy level1) Mg 2) Ca 3) Na


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Valence ElectronsValence Electrons

Valence or outer shell, or outermostelectrons, are the electrons filling the lastlevel of energy in a given atom

Indicate the number of valance electrons:A. O 1) 4 2) 6 3) 8

B. Al 1) 13 2) 3 3) 1

C. Cl 1) 2 2) 5 3) 7


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Periodic LawPeriodic Law

All the elements in a group have the sameelectron configuration in their outermostshells

Example: Group 2A

Be 2, 2Mg 2, 8, 2

Ca 2, 8, 8, 2

Specify if each pair has chemical properties

that are similar (1) or different (2):

A. Cl and Br B. 2 - 5 and 2 - 8 -7

C. 2 - 4 and 2 - 8 4 D. P and S


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9. Electron Configurations and the Periodic Table9. Electron Configurations and the Periodic Table

- Note that the 3dorbital fills after the 4s orbital.

- Similarly, the 4forbital fills after the 5dorbital.

SiV


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Electron Configurations and the Periodic TableElectron Configurations and the Periodic Table

There is a shorthand way of writing electron configurations

Write the core electronscorresponding to the filled Noble gasin square brackets.

Write the valence electrons explicitly.

Example, P: 1s22s22p63s23p3

but Ne is 1s2

2s2

2p6

Therefore, P: [Ne]3s23p3.


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Electron ConfigurationsElectron Configurations

There are a coupleexceptions due to morestable electronconfiguration:

Cr group prefers to have ahalf filled nd orbital with 5electrons Cr: [Ar] 4s2 3d4 becomes

Cr: [Ar] 4s1 3d5

Cu group prefers to have acompletely filled nd orbitalwith 10 electrons

C [A ] 42

3d9

b

2 atomic structure b kartic

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