Preliminary Course: Atomic Structure Lankani Wijesinghe

Outline

PART 1

• What is Matter?

• History of the atomic structure

• Atomic model

PART 2

• Introduction to the periodic table

• Properties of some main group elements

• Ions

Why learn atomic structure ?

Classification of matter

Classification of matter

Classification of matter

Different kinds of Atoms: The Elements

To Democritus, atoms were small, hard particles that were all made of the same

material but were different shapes and sizes. Atoms were infinite in number, always

moving and capable of joining together.

Atomic Theory of Matter

To Democritus, atoms were small,

hard particles that were all made of

the same material but were different

shapes and sizes.

Atoms were infinite in number,

always moving and capable of

joining together.

Atomic Theory of Matter

The billiard ball

Law of Multiple Proportions

The atomic theory makes sense!

Atomic Structure: Electrons

• J.J.Thompson (1897) applies

voltage to gas in a sealed tube

•Cathode rays are negatively

charged

•The charged particles which are

produced are found to have a

mass 1800 times smaller than

hydrogen

Plum pudding model

Thompson postulated that the negative particles reside within atoms,

balanced by a “delicious cake” of positive charge.

Beyond the Plum Pudding

Beyond the Plum Pudding

Rutherford's conclusions

Bohr’s Atom

Neils Bohr (1885–1962) refined Rutherford's

model in 1913 by proposing that electrons:

- orbit the nucleus without losing energy;

- could move only in fixed orbits of specific

energies.

- electrons with low energy would orbit closer to

the nucleus while electrons with high energy

orbit further from the nucleus.

Rutherford's –Bohr’s Atom

The neutron is discovered

The Atomic Model

The Nuclear Atom

Atomic Number

Mass Number

Isotopes

An example: Heavy water

Birth of the Periodic Table

Also took in to consideration

• density

• melting point

• reactivity

Mendeleev’s Periodic Table (1869)

Mendeleev’s Periodic Table (1871)

The Modern Periodic Table

The Modern Periodic Table

Metals, Non-Metals and Semi-Metals

Metals • conducts electricity • has a metallic lustre • malleable and ductile

Non-metals

• lack metallic lustre • does not conduct electricity - good insulators • brittle

Semi-metals (metalloids)

• It has some properties like a metal and some properties are like a non-metal

Na Au

C

Hg

Br

Si Ge

Metals, Non-Metals and Semi-Metals

Group 1: Alkali metals

• Soft, silvery metals

• Low melting points

• Very reactive with air and water

• Produces H2 when reacted with water

• Reactivity increases down the group

• One electron in the valence shell

Group 2: Alkaline earth metals

• Silvery metals

• Less reactive than alkali metals

• Produces H2 when reacted with water

• Reactivity increases down the group

• Two electrons in the valence shell

Group 17: Halogens

Cl Br I

• Chemically reactive

• Found in salts

• Used as disinfectants (eg. Cl, Br, I)

• Form acids when bonded to hydrogen (eg. HCl, HF)

• 7 electrons in the valence shell

Group 18: Noble gases

• Colourless, ordourless gases

• Highly unreactive

• Only heavier noble gases undergo some chemical

reaction

• Electronically stable

Electron discharge colour

Transition metals

Transition metals

Chemistry is all about electrons

Sodium wants to lose an electron!

(Na+)

Metals generally form CATIONS

Cu+, Cu2+ etc.

Chlorine wants an electron!

(Cl-)

Non-metals generally form ANIONS

Cations and Anions stick together

GOOD LUCK WITH YOUR FIRST YEAR AT TRINITY COLLEGE DUBLIN !!