1 - Elements and the Periodic Table

Complete past exam questions after you have gone through these cards

Mixture

Two or more substances mingled together but not chemically combined

Compound

Two or more elements chemically combined

Molecule

Two or more atoms chemically combined

Element

Substance that cannot be broken down into anything simpler by chemical means

What was a triad of elements according to Dobereiner?

Give an example

Elements that have similar chemical properties //

atomic mass of middle element is average of the other two

e.g. Li, Na, K

What contribution did Newlands make to the systematic arrangement of the elements?

Arranged in increasing relative atomic mass / octaves

How did Mendelev arrange the elements to form his periodic table?

Elements listed in order of increasing atomic mass //

Elements with similar chemical properties were listed in columns //

left gaps

Suggest a reason why Mendelev did not suspect the existence of argon

Noble gases were unknown (undiscovered) /

inertness of argon (noble gases) /

no gap for argon

Comment on the positioning of tellurium (Te) and iodine (I) in the 1869 table.

listed correctly according to chemical properties /

chemical properties matched better when order reversed

Give an advantage of arranging the elements in order of increasing atomic number

more fundamental property of element /

no need to reverse order to force elements into correct groups /

tellurium (Te) and iodine (I) in correct groups /

indicates undiscovered elements

Explain why all the elements of Group 18 in the periodic table are chemically inert

Stable arrangement of electrons / do not lose or gain electrons / satisfy octet rule

Explain how and why the reactivity of the halogens changes down Group 17

How: less reactive down group / less likely to gain an electron down group

Why: increasing atomic radius / more shells / nucleus farther from outer electrons / increasing screening / more difficult to achieve full outer sub-level / decreasing electronegativity

In the periodic table, identify an element

i) in the same period as magnesium but with larger atoms,

ii) in the same group as magnesium but with smaller atoms

i) Sodium (Na) //

ii) Beryllium (Be)

Mendelev predicted the properties of the elements gallium and germanium years before either of them was discovered. Explain the basis for his predictions

Having arranged elements in order of increasing atomic weight /

where elements with similar properties were arranged in columns /

left gaps for elements with certain properties yet to be discovered

Explain why

i) the alkali metals are all reactive

ii) the reactivity of the alkali metals increases down the group

i) Readily lose single electron / low first ionisation energy

ii) Increase in atomic radius / atoms getting bigger / decrease in first ionisation energy / outer electron more easily lost

State two differences between Mendelev’s periodic table and the modern periodic table of the elements