chapter 4 periodic table of elements

Chapter 4: Periodic Table of Elements

4.1 The Periodic Table of Elements

1. Antoine Lavoisiera. First scientist to classify elements into four groups based on their similar

properties. (metal, non-metal, gases and earth)b. Unsuccessful because light, heat and few other compounds were also considered

as elements.2. Johann Dobereiner

a. Divide the similar chemical properties elements into groups called “Triads”.b. Unsuccessful because it was limited to some elements only.

3. John Newlands a. Arranged the known elements in order of increasing atomic mass.b. Divided the elements into groups of seven, as he founded every eighth element

had properties similar to the first element of the preceding series.c. Law of octaves – The eighth element, starting from a given one, is a kind of

repetition of the first, like the eighth note of an octave in music.d. It was only accurate for the first 17 elements.

4. Lothar Meyera. Plotted a graph of the atomic volume against the atomic mass, and stated that the

atomic volume of an element is the relative atomic mass divided by the density of the element.

b. Several statements were pointed out from the graph (similar chemical properties)i. The alkali metals are at the peaks of the curve. (Li, Ma, K, Rb)

ii. The halogens are just before the peaks. (F, Cl, Br)iii. Na, Ca and Sr (Strontium) come immediately after the peaks.

5. Dmitri Mendeleeva. Arranged the elements in order of increasing atomic mass and grouped them

according to similar chemical properties.b. Left some spaces yet to be discovered.

6. H. J. G. Moseleya. Discovered the proton number of elements by studying the frequency of the X-

ray produced by each element.b. He concluded that proton number should be the basis for the periodic change of

chemical properties instead of the atomic mass.c. He arranged the elements in order of increasing proton number in periodic table.

7. In the modern Periodic Table, elements are arranged in order of increasing proton number.

a. Vertical columns – “Group” (Group 1 to 18)i. Group 1 – Alkali Metals

ii. Group 2 – Alkaline Earth Metalsiii. Group 3 to 12 – Transition metals 过度金属iv. Group 17 – Halogens 卤素v. Group 18 – Noble gases, as known as Inert gases

b. Horizontal rows – “Period” (Period 1 to 7)i. Period 1 consists of 2 elements: H and He.

ii. Period 2 consists of 8 elements: Li ~ Ne.iii. Period 3 consists of 8 elements: Na ~ Ar.iv. Period 4 and 5 have 18 elements respectively.v. Period 6 consists of 32 elements

1. Elements with proton numbers 58 to 71 are categorized as “Lanthanides”. 镧系元素

vi. Period 7 1. Elements with proton numbers 90 to 103 are categorized as

“Actinides”. 锕系元素

SPM Chemistry Form 4


8. Metals are placed on the left-hand side of the Periodic Table.a. All metals are solid at room temperature except Mecury.b. Most metal are silvery, generally malleable, and also good conductors of heat and

electricity.9. Non-metals are placed on the right-hand side of the Periodic Table.

a. Eleven of the non-metals are gases, one is liquid (Bromine) and only six are solids (C, P, S, Se, I and At) at room temperature.

b. Solid non-metals are brittle and they are poor conductors of heat and electricity.10. Seven elements adjacent to the boundary between metals and non-metals are known as

semi-metals or metalloids. (B, Si, Ge, As, Sb, Te, Po)a. Obtain both metal and non-metal properties.b. Most semi-metals are silvery solid at room temperature, but they are brittle rather

than malleable and tend to be poor conductors of heat and electricity.11. Information from Periodic Table.

a. The properties of elements in a GROUP become more METALLIC when going DOWN the group.

b. Elements that are GASES at room temperature are placed on the top right-hand corner.

c. In any group, the atomic sizes of elements INCREASE DOWN the group.d. In any period, the atomic sizes of elements DECREASE across the period from

LEFT to RIGHT.12. The number of valence electrons (价电子) in an atom decides the position of the GROUP

of the Periodic Table. Meanwhile, the number of shells occupied with electrons in an atom determines the PERIOD number of an element.

13. Advantages of Periodic Table.a. Classify elements in a more systematic way, helping us to understand the

elements better.b. Using the properties of elements in a group therefore we are able to make

prediction about elements that we have probably never seen.

4.2 Group 18 Elements

1. 6 elements in Group 18: Helium, Neon, Argon, Krypton, Xenon and Radon.2. Physical properties

a. Exist as monoatomic (单原子组成的分子) gases.b. Colourless gases at room temperature.c. Insoluble in water.d. Cannot conduct electricity and poor conductors of heat.e. Small atomic sizes.f. Low melting and boiling points. (Because of the weak Van der Waals forces)g. Low densities.

3. When going down the Group 18,a. The atomic size INCREASES, as the number of occupied shells in the atom

increases down the group.b. The melting point and boiling point INCREASE, as the atomic size increases

down the group, the forces of attraction between the atoms of each element become stronger. Thus more heat energy is required to overcome the stronger forces attraction during melting or boiling.

c. The density of element INCREASES, as the increase in relative molecular mass is more than increase in atomic size down the Group 18.

4. The outermost occupied shell is FULL of electrons.a. Helium has 2 valence electrons, known as “duplet electron arrangement”.b. Other noble gases have 8 valence electrons, known as “octet electron

arrangement”.



c. The electron arrangement is STABLE therefore noble gases are chemically UNREACTIVE or known as inert.

5. Uses of inert gasesa. Helium

i. Fill airships or weather balloonsii. Gas breathed by divers.

iii. Liquid Helium – cool down metals to a very low temperature.b. Neon

i. Advertising lights and television tubes.ii. Billboards light. (Neon glows with a reddish orange colour when it met

high voltage)c. Argon

i. Fill light bulbs (not react with tungsten metal filament in the bulb)ii. Used during certain welding (焊接) process.

d. Krypton i. Used in lasers in medical industry.

ii. Fill photographic flash lamps.e. Radon

i. It is radioactive and used to treat cancer.

4.3 Group 1 Elements

1. It is also known as “Alkali Metals”.2. The outermost shell of each element of Group 1 contains 1 valence electron.3. Physical properties

a. Good conductors of heat and electricity.b. Soft and can be cut easily with knife.c. Grey in colour with silvery and shiny surfaces when freshly cut.d. Low densities and float on water.

4. When going down Group 1,a. The atomic size INCREASES, as the number of shells occupied with electrons

increases. Hence the distance between the outermost shell occupied with electrons and the nucleus becomes further.

b. The melting and boiling points DECREASE, as the atomic size increases, the forces of metal atoms become weaker. Hence less heat energy is required to overcome the weak forces of attraction.

c.


chapter 4 periodic table of elements

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