Atomicstructureppt 140315053706-phpapp02

CHEMISTRY PROJECTB

YCOMPUTE

R CAREERS

ATOMIC STRUCTURE

What is an Atom?

• Matter is anything that takes up space and has mass.

• All matter is made of atoms

• Atoms are the building blocks of matter, sort of how bricks are the building blocks of houses.

Parts of Atom• An atom has three parts:

• Proton = positive

• Neutron = no charge

• Electron = negative

• The proton & neutron are found in the center of the atom, a place called the nucleus.

• The electrons orbit the nucleus.

ATOMIC STRUCTUREATOMIC STRUCTURE

Electrons are arranged in Energy Levels

or Shells around the nucleus of an atom.

• first shell a maximum of 2 electrons

• second shell a maximum of 8

electrons

• third shell a maximum of 8

electrons

ATOMIC STRUCTUREATOMIC STRUCTURE

There are two ways to represent the atomic

structure of n element or compound;

1. Electronic Configuration

2. Dot & Cross Diagrams

ELECTRONIC CONFIGURATIONELECTRONIC CONFIGURATION

With electronic configuration elements are

represented numerically by the number of

electrons in their shells and number of shells.

For example;

NNitrogen

14

2 in 1st shell

5 in 2nd shell

configuration = 2 , 5

2 + 5 = 7 7

DOT & CROSS DIAGRAMSDOT & CROSS DIAGRAMSWith Dot & Cross diagrams elements and

compounds are represented by Dots or

Crosses to show electrons, and circles to

show the shells. For example;

Nitrogen N XX X

X

XX

X N7

14

1910

Ernest Rutherford

oversaw Geiger and Marsden carrying

out his famous experiment.

they fired Helium nuclei at a piece of

gold foil which was only a few atoms

thick.

they found that although most of

them passed through. About 1 in

10,000 hit

Rutherford’s InventionRutherford’s Inventiongold foil

helium nuclei

They found that while most of the helium nuclei

passed through the foil, a small number were

deflected and, to their surprise, some helium

nuclei bounced straight back.

helium nuclei

Rutherford’s new evidence allowed him

to propose a more detailed model with a

central nucleus.

He suggested that the positive charge

was all in a central nucleus. With this

holding the electrons in place by

electrical attraction

However, this was not the end of the story.

ARISEN OF NEILS BOHRARISEN OF NEILS BOHR

1913

Niels Bohr

studied under Rutherford at the Victoria

University in Manchester.

Bohr refined Rutherford's idea by

adding that the electrons were in

orbits. Rather like planets orbiting the

sun. With each orbit only able to

contain a set number of electrons.

Rutherford’s alpha scattering experiment

source of

alpha particles

Thin gold foil

Photographic film

Beam of particles most

pass straight

through

1 in 20 000 deflected

Rutherford’s explanation

atoms of gold

in gold foil

Path of an particle

nucleus of

gold atom

All these particles pass straight through the empty space that makes up most of the atom.

This particle

passes close enough to nucleus to be repelled

As particles are positively charged, the nucleus must contain positively

charged protons.

atoms of gold

in gold foil

nucleus of

gold atom

As only 1 in every 20 000 particles are repelled the nucleus must be very small.

Size of the nucleus

Rutherford’s model of the atom

Tiny nucleus containing the positively charged protons.

Rest of atom is mostly empty space. The negatively charged

electrons are spinning round the nucleus.

Section 3.1

The Limitations of Rutherford’s Atomic Model

Chapter 3: Atomic Models and Properties of Atoms

• radiation must be emitted, so it was expected that a continuous spectrum of light energy was being given off

• because of radiation, the electron would lose energy and its orbit would decrease until it spiraled into the nucleus, destroying the atom

Bohr Model of Atom• The Bohr Model shows

all of the particles in the atom.

• In the center is circles. Each circle represents a single neutron or proton. Protons should have a plus or P written on them. Neutrons should be blank or have an N.

• In a circle around the nucleus are the electrons. Electrons should have a minus sign or an e.

++++

--

--

Bohr’s Atomelectrons in orbits

nucleus

Bohr's Model of the Atom

Bohr's model:-electrons orbit the nucleus like planets orbit the sun

-each orbit can hold a specific maximum number of electrons

-electrons fill orbits closest to the nucleus first.


Niels Bohr (1913):-studied the light produced when atoms were excited by heat or electricity

Rutherford's model couldn't explain why unique colours were obtained by atoms of different elements

Bohr proposed that electrons are in orbits & when excited jump to a higher orbit. When they fall back to the original they give off light


e.g. fluorine:#P =

#e- =

#N =

9

9

109P

10N

http://education.jlab.org/atomtour/fact3.html

Today’s quantum mechanical model of the atom incorporates the wave properties of electrons.

Section 3.2

The Quantum Mechanical Model of the Atom

An electron density diagram represents an atomic orbital.


Wave functions, initially described by Erwin Schrodinger, represent a region in space around a nucleus where an electron will be found. This region of space is called an atomic orbital

Section 3.2

The Quantum Mechanical Model of the Atom

The circle does not represent a real boundary.


Atomic orbitals can be visualized as “fuzzy clouds”

• The higher the density of the “cloud,” the higher the probability of finding an electron at that point.

• The cloud has no definite boundary.• The region where an electron will spend 90

percent of its time is depicted by drawing a circle.

Section 3.1

Quantum Numbers Describe Orbitals


Electrons in the quantum mechanical model of the atom are described using quantum numbers.Three quantum numbers describe the distribution of electrons in the atom and a fourth describes the behaviour of each electron.

Symbols for the four quantum numbers:

n l ml ms

Section 3.2

The Principle Quantum Number, n


• Is the first quantum number• Describes the energy level, or shell, of an

orbital• All orbitals with the same n value are in the

same shell• The larger the n value, the larger the size of the

shell• Values can range from n = 1 to n = ∞

n = 1 first shelln = 2 second shelln = 3 third shelln = 4 fourth shell

Section 3.2

The Orbital-Shape Quantum Number, l


• Is the second quantum number• Describes the shape of an orbital• Refers to energy sublevels, or subshells• Values depend on the value of n. They are positive

integers from 0 to (n – 1)• Each value is identified by a letter

l = 0 orbital sl = 1 orbital pl = 2 orbital dl = 3 orbital f

An energy sublevel is identified by combining n with the orbital letter. For example, n = 2, l = 1: 2p sublevel

Section 3.2

The Magnetic Quantum Number, ml

s, p, and d orbitals have characteristic shapes.


• Is the third quantum number • Indicates the orientation of the orbital in space• For a given l there are (2l +1) values for ml• The total number of orbitals for an energy level

is n2

NucleusNucleus

11stst shell shell

22ndnd shell shell

33rdrd shell shell

Atomicstructureppt 140315053706-phpapp02

Documents

Transcript of Atomicstructureppt 140315053706-phpapp02