Particulate Nature Of Matter And Atomic Structure

Front 1

Democritus

Back 1

A Greek philosopher (400Bc) was the first to show that matter is made up of small particles called atoms

Front 2

Atom

Back 2

Is the smallest particle of an element which can take part in a chemical reaction

Front 3

Molecule

Back 3

Is the smallest particle of an element or compound which can exist on it own. It is made up of two or more atoms of the same or different elements

Front 4

John Dalton

Back 4

Was the first to present a convincing experimental evidence to support the atomic theory

Front 5

Atomic theory

Back 5

1-matter is made up of small or tiny indivisible particles called atom.

2-all atoms of a particular element are exactly alike in size,shape and mass but are different from atoms of other elements

3-in chemical reactions whole atom(never fraction) combine,separate or change places

4-when atoms combine with one another they do so in small whole number ratio

Front 6

Concept of relative atomic mass

Back 6

Atom is so small that it cannot be seen with microscope. Hence chemist accepted the this concept which enables the masses of atoms of various elements to be compared. Carbon-12 is the reference standard and has been assigned 12.0 atomic mass unit. The relative atomic mass unit of other elements are estimated relative to that of carbon-12 using the mass spectrometer invented by aston1919.the relative atomic mass has no unit, it is a ratio

Front 7

Relative atomic mass

Back 7

Is the average mass of one atom of an element on a scale in which one atom of carbon-12 weighs 12 atomic mass unit(a.m.u)

Front 8

Relative molecular mass of an element or a compound

Back 8

Is the average mass of one molecule of an element or compound on a scale in which one atom of carbon-12 weighs 12 a.m.u

Front 9

Composition of the atom

Back 9

An atom has two main parts, the nucleus(center) and the shells which surround the nucleus at definite distance

Front 10

Subatomic particles

Back 10

An atom is composed of three subatomic particles which include protons and neutrons(nuclear particles) found in the nucleus while the electrons are in constant and continuous motion in the shells at various energy levels

Front 11

Relative masses and electrical charges of the atomic particles

Back 11

1-Proton has a relative mass of 1 and a +ve charge

2-neutron has a relative mass of 1 and no charge(neutral)

3-electron has a relative mass of 1/1840 and a -ve charge

The mass of an atom is concentrated in the nucleus while the electron contribute least to the mass of an atom

Front 12

Atomic number

Back 12

Is the number of protons in the nucleus. It is equal to nuclear charge and is always a whole number

An atom is electrically neutral because the number of protons in the nucleus is equal to the number of electrons in the shell

Front 13

Mass number

Back 13

Is the sum of the number of protons and neutrons in the nucleus

Front 14

Concept of isotopy

Back 14

Scientific discoveries shows that some elements are made up of two or more types of atoms with different atomic masses,such a phenomenon is called isotopy and this is contrary to one of the postulates of Dalton's atomic theory

Front 15

Isotopes or nuclides

Back 15

Are atoms of the same element with the same atomic number but different mass number or atoms of the same element with the same number of protons but different neutron number

Front 16

Relative atomic masses of isotopic elements

Back 16

The relative atomic mass of an element with two or more isotope depends on the relative or percentage abundance of each isotope in the element and for an element that has only one type of atom or no isotope, the mass number is equal to the relative atomic mass

Front 17

Relative atomic masses of isotopic elements

Back 17

The relative atomic mass of an element with two or more isotope depends on the relative or percentage abundance of each isotope in the element and for an element that has only one type of atom or no isotope, the mass number is equal to the relative atomic mass

Front 18

Mass spectrometer

Back 18

Is a device that is used to determine the number of isotopes of an element and their relative abundance

Front 19

Uses of the mass spectrometer

Back 19

1-to determine the relative atomic mass of an elements

2-to determine the relative abundance of elements

The number of peaks on the x-axis corresponds to the number of isotopes while the height of peaks on the y-axis is directly proportional to the relative abundance of the isotope

Front 20

Shells and energy level

Back 20

Shells are represented by the capital letters K,L,M,N. The shell nearest to the nucleus or the innermost shell is the K-shell followed by the L-shell,then the M-shell,then N-shell

Front 21

Shells

Back 21

Shells are represented by the capital letters K,L,M,N. The shell nearest to the nucleus or the innermost shell is the K-shell followed by the L-shell,then the M-shell,then N-shell

Front 22

Energy level

Back 22

Each shell is at an energy level represented by the principal quantum number(n).the K-shell is in the first energy level where n=1,it has the lowest energy,the L-shell is in the second energy level n=2, M-shell is in the third energy level n=3 while the N-shell is in the fourth energy level n=4.

The higher the principal quantum number the higher the energy level and the farther away the shell from the nucleus

Front 23

Shell electron configurations

Back 23

Indicates the number of electrons in the various Shell or energy level of an element. The maximum number of electrons that a shell or energy level can accommodate is limited by the formula 2n^2.the K-shell where n=1 can accommodate a maximum of two electrons,L-shell where n=2 can accommodate maximum of eight electrons,M-shell where n=3 can accommodate maximum of eighteen electrons and N-shell where n=4 can accommodate 32 electrons but considering the first twenty elements the M and N shell can also accommodate eight electrons instead of eighteen and thirty two by calculations. When filling the shells, the K-shell is filled first followed L-shell,M-shell then N-shell

Front 24

Energy sublevels

Back 24

Each shell has one or more sub-shells which are at energy sub-levels represented by the small letters s,p,d,f. The number of sublevels in an energy level equals the value of n.

The K-shell has only one sublevel called 1s sublevel, the L-shelk has only two called 2s and 2p sublevels, M-shell has only three called 3s,3p and 3d sublevels, N-shell has only four called 4s,4p,4d and 4f sublevels

Front 25

Orbitals

Back 25

An orbital is a region around the nucleus where electrons are found. Each energy sublevel has one or more orbitals. An s-sublevel has one orbital called s-orbital,p-sublevel has three orbitals called p-orbitals,d-sublevel has five orbitals called d-orbitals and f-sublevel has seven orbitals called f-orbitals. The total number of orbitals in a particular sublevel is limited by the formula n^2.an orbital can accommodate a maximum of two electrons

Front 26

Principles that govern the order in which electrons enter the orbitals in the various energy level include

Back 26

1-aufbau principle

2-Pauli exclusion principle

3-hund's rule of maximum multiplicity

Front 27

Aufbau principle(order of increasing energy )

Back 27

Aufbau means building up and it states that electrons enter into orbitals in order of increasing energy

Front 28

Ground state electronic configuration

Back 28

Is when electrons occupy the energy sublevel according to aufbau principle. It is the most stable state of an atom

Front 29

Pauli exclusion principle(electron spin)

Back 29

States that an orbital can accommodate two electrons of opposite spin(up and down spin or clockwise and anticlockwise spin).this is in order to minimize repulsion within the orbital

Front 30

Hund's rule of maximum multiplicity(degenerate orbitals)

Back 30

Electrons will occupy degenerate orbitals singly with the same spin or no pairing in degenerate orbitals until each orbital is singly occupied with parallel spin

Degenerate orbitals are those that have the same energy or in the same energy level

Front 31

Valence shells

Back 31

Is the outermost shell of electrons in the electronic configuration of an atom of an element and the electrons in the valence shells are called valence electron

Front 32

Noble or rare gas configuration

Back 32

Is an electron configuration in which the last atom of an element complete the valence shell.

Front 33

Noble or rare gas configuration

Back 33

Is an electron configuration in which the last electron of an element complete the valence shell.

Front 34

J.j Thompson(1897)

Back 34

Discovered the existence of electrons in the atoms from his cathode ray experiment.in his model of atom,he described an atom as a uniform density ball of positively charge mass with electrons scattered randomly within the sphere

Front 35

Cathode rays

Back 35

Are stream of negatively charged particles moving in a straight line with a high velocity from the cathode to the anode. They are also called electrons

Front 36

R.A Millikan(1909)

Back 36

Used the oil-drop experiment to determine the value of charge on an electron which was found to be 1.6×10^-19 coulombs

Front 37

Goldstein (1886)

Back 37

Discovered the presence of positively charged particles in the discharge tube which are produced when electrons are removed from neutral gaseous atoms.such particles are called positive ion or cations and are attracted towards the negative cathode in the discharged tube.when positive ions are allowed to pass through a perforated cathode they form positive rays

Front 38

Lord Ernest rutherford(1911)

Back 38

Observed that the total mass of the protons and electrons in an atom is not equal to the actual mass of the atom as obtained from the mass spectrometer and that the total mass of the protons in an atom account for about half of the nuclear mass of the atom.therefore he suggested the presence of another particle in an atom

Front 39

Rutherford model of the Atoms

Back 39

1-an atom contains a small massive and positive center called the nucleus which contains the protons and neutrons.it is responsible for the entire mass of the atom and that the volume occupied by the nucleus is very small compared to the entire volume of the atom

2-the electrons rotate round the nucleus in the same way that the planet rotate around the sun

Front 40

Rejection of Rutherford's model of the atom

Back 40

Scientist accepted the existence of the positively charge nucleus in an atom but rejected his idea of planetary electrons.this is because Rutherford's model could not explain why electrons being negatively charge and in continuous motion will not be losing energy,slow down,move spirally nearer to the nucleus and be captured finally by the nucleus(I.e for an atom to collapse)

Front 41

James Chadwick(1932)

Back 41

Discovered the existence of a new particle which carries no charge(I.e it is neutral) and has a mass almost equal to that of proton.this new particle is called neutron and it account for about half the nuclear mass. All elements have neutron except a naturally existing hydrogen called protium

Front 42

Bohr's theory of the atom

Back 42

Niel bohr (1913) used the quantum theory developed by Maxwell Planck and Einstein to account for the spectrum of hydrogen.he made the following postulates

1-electrons exist only in distinct energy levels and never between energy level and that the energy levels are at definite distance from the nucleus.

2-the energy of an electron in a particular energy level has a fixed value or quantized and is different from that of an electron in another energy level.

3-an electron continues to orbit round the nucleus in a particular energy level at a given temperature without losing energy

4-when an atom absorbs sufficient energy it electrons can be promoted from lower to higher energy level.when a promoted electron falls from a higher to a lower energy,a quantum radiation is emitted and the radiation produces a line in the emission spectrum of the element.

5-when an electron is in the lowest energy or at the level nearest to the nucleus,it does not emit energy when orbiting round the nucleus.for this reason electron cannot be captured by the nucleus (I.e an atom cannot collapse)

Front 43

Electron transition

Back 43

Is the process whereby an electron moves from one energy level to another within the atom.the energy associated with quantum radiation in an electronic transition is the energy difference between the higher and lower energy levels

Front 44

Wave and particulate character of an electron

Back 44

From the study of atomic structure de Broglie suggested that an electron apart from being a particle,has a wave character (dual character) because a beam of electrons has mass and can undergo diffraction and further studies on the atom shows that electrons do not move in definite path like the earth orbits round the sun

Front 45

Heisenberg uncertainty principles

Back 45

According to this principle,it is impossible to know the exact position and velocity of a small moving body such as an electron.instead one can only give the probability of finding an electron in a given volume.the region in space where there is a high probability or chance of finding an electron is called the orbit.the distribution of electron density around the nucleus forms the electron cloud which gives the shape and size of an orbital

Front 46

Quantum numbers

Back 46

The Electrons in an orbital can be identified by four quantum number.

1-principal quantum number(n)

2-angular momentum(azimuthal)quantum number(I)

3-magnetic quantum number(m)

4-spin quantum number (Ms)

Front 47

Principal quantum number

Back 47

There are energy levels in an atom and each energy level has its own principal quantum number(n) which is a positive integer.the value of n determines the relative energy of an electron and it's average distance from the nucleus and as the value of n increases energy also increase with a simultaneous increase in the distance from the nucleus. It also determines the size of an orbital,the higher the n value the larger the size of the orbital. Energy levels are also called shell represented by capital letter K,L,M,N etc

Front 48

Angular momentum or azimuthal quantum number

Back 48

Each energy level has one or more energy sublevels.each sublevel has it own sublevel quantum number,l,which can take the values 0,1,3,4 etc and each sublevel has it own symbol s,p,d,f written in small letters.the number of sublevels in an energy level is equal to the value of the principal quantum number of the sublevel.the value of the sublevel quantum numbee ,l,starts from zero and positive integers up to a maximum of (n-l).the value of l determines the shape of the orbital

Front 49

Magnetic quantum number

Back 49

Each energy sublevels have one or more orbitals.the number of orbitals in a sublevel is determined by the value of the sublevel quantum number l, it is equal to the mathematical formula 2l+1.each orbital has it own orientation in space and is represented by magnetic quantum number, m,which has values ranging from +1to-1 including zero.the maximum number of orbitals in an energy level is limited by the formula n^2

Front 50

Spin quantum number

Back 50

The spinning of an electron about its own axis in an orbital is due to its magnetic property. The two direction of spin are clockwise and anticlockwise.the spin is designated by the spin quantum number +1/2 or -1/2.the maximum number of electrons in an energy level or shell is limited by the formular 2n^2

Front 51

S-orbital

Back 51

An s-sublevel Has only one orbital called s-orbital.it is spherically symmetrical about the nucleus.it size and energy depends on the principal quantum number.the higher the n value the larger the orbital size and the higher it energy.

Front 52

P-orbitals

Back 52

The p-sublevel has three orbitals called p-orbitals and each orbital has a dumbbell shape(like figure eight) with the electron density concentrated on both side of the nucleus(the node).the three p-orbitals lie at right angle to one another(i.e they are mutually orthagonal).they are designated Px,Py and Pz

Front 53

Roentgen

Back 53

In 1885 discovered that when high energy electrons In a discharge tube collide with the anode,a penetrating radiation which he called X-rays is produced

Front 54

Moseley

Back 54

In 1914,found that he could assign a number called atomic number based on the frequency of the X-rays the elements emit when it is used as the anode of an X-ray tube .further experiments enabled Mosley to conclude that the atomic number represents the number of protons in the nucleus

Front 55

Modification of Dalton's atomic theory

Back 55

1-it has been found that atoms is made up of three fundamental particles(protons,neutrons and electrons).it is not the smallest indivisible piece

2-the discovery of radioactivity has shown that atoms can be created or destroyed e.g during nuclear fission. but the postulate still hold good for ordinary chemical reactions and is embodied in the basic law of conservation of mass.

3-the concept of isotopy has shown that all atoms of an element are not exactly alike.

4-it has been found that organic combination between atoms could be large whole numbers.but the postulate is generally true for inorganic compounds which contains few atoms per molecule

Front 56

Formulae for calculating mean relative atomic mass of isotopes

Back 56

Mr =(A1 + P1 )+( A2 + P2 )

--------------------------------

P1 + P2