C4 - OCR 21st Century Science - Chemical Patterns

Notes for Chemistry C4 - OCR

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C4 ­ Chemical Patterns ­ Answers
1. In the Periodic Table, the elements are arranged in order of proton number, also called atomic number. This is
the number of positive protons in each atom. It is shown as the number written below each element in the table
below. Putting elements in this order gives a repeating pattern of their properties. In the Periodic Table each
element is placed beneath those with similar properties. This helps us to make sense of the different properties
of the elements and their compounds. It also helps us to predict how they will behave in different situations.
2. Each column in the table contains elements with similar properties, called a group. Each has a group number,
shown across the top of the table. So Group 1 contains the elements lithium (Li) to francium (Fr), and Group 7
contains the elements fluorine (F) to astatine (At). Because there are patterns in the way the elements are
arranged in the Periodic Table, it can be used to predict their properties and interpret data.
3. A period is a row in the periodic table. Across each row, the elements on
the left are metals, while those on the right are non-metals. In a row
across the Periodic Table, the elements get less metallic as we go from
left to right. This can be used to predict how a particular element will
behave. Each period starts with a very reactive metal in group 1 and ends
with an unreactive gas in group 8.
4. It is a comparative measurement of the mass of one atom of the element.
It shows everything in comparison to one atom of hydrogen. You can use it
to see how much heavier an atom of one element is compared with an atom of another element. For example a
magnesium atom has a relative atomic mass of 24. So we know it is twice as heavy as a carbon atom, which has a
relative atomic mass of 12.
5. The elements in Group 1 of the Periodic Table are called the alkali metals. They are lithium (Li), sodium (Na),
potassium (K) Rubidium (Rb), Caesium (Ca) and Francium (Fr).
6. Physical Properties of the Alkali Metals:
Reaction in air - Lithium, sodium and potassium are all soft metals that are easily cut with a scalpel or knife.
The freshly cut surface is a shiny, silver colour, but this tarnishes quickly to a dull grey as the metal reacts with
oxygen and water in the air. Pieces of such metals are stored in oil to prevent these reactions. The shiny
surface of sodium tarnishes more quickly than that of lithium. And potassium tarnishes more quickly than
sodium. This shows the increasing reactivity of the metals as we go down the group.
Melting and Boiling Points - The alkali metals have low melting and boiling points compared to most other
metals. Lithium, at the top of Group 1, has the highest melting point in the group. The melting points then
decrease as you go down the group. The boiling points of these alkali metals show a similar pattern to the
melting points.
Density - The alkali metals have low densities compared to most other metals. (They feel lighter.) The top of
Group 1 has the lowest density in the group. The densities then generally increase as you go down the group.
Hardness - Lithium, sodium and potassium are all soft metals that are easily cut with a scalpel or knife. Lithium
is the hardest alkali metal and they become softer as you go down the group.
7. All the alkali metals react vigorously with cold water. In each reaction, hydrogen gas is given off and the metal
hydroxide is produced. The speed and violence of the reaction increases as you go down the group. This shows
that the reactivity of the alkali metals increases as you go down Group 1.
Lithium - When lithium is added to water, lithium floats. It fizzes steadily and becomes smaller, until it
eventually disappears.
Sodium - When sodium is added to water, the sodium melts to form a ball that moves around on the surface.
It fizzes rapidly, and the hydrogen produced may burn with an orange flame before the sodium disappears.
Potassium - When potassium is added to water, the metal melts and floats. It moves around very quickly on
the surface of the water. The hydrogen ignites instantly. The metal is also set on fire, with sparks and a lilac
flame. There is sometimes a small explosion at the end of the reaction.
8. All of the alkali metals react vigorously with chlorine gas. Each reaction produces a white crystalline salt. The
reaction gets more violent as you move down Group 1, showing how reactivity increases down the group.

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Lithium - If a piece of hot lithium is lowered into a jar of chlorine, white powder is produced and settles on the
sides of the jar. This is the salt lithium chloride. 2Li(s) + Cl2(g) 2LiCl(s)
Sodium - If a piece of hot sodium is lowered into a jar of chlorine, the sodium burns with a bright yellow flame.
Clouds of white powder are produced and settle on the sides of the jar. This is the salt sodium chloride.…read more

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This type of reaction happens with all of the halogens. A more reactive halogen displaces a less reactive halogen
from a solution of one of its salts. The most reactive halogen displaces all of the other halogens from solutions of
their salts, and is itself displaced by none of the others. The least reactive halogen displaces none of the others,
and is itself displaced by all of the others. It works just the same whether you use sodium salts or
potassium salts.
19.…read more

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The force of attraction between the positively-charged nucleus and the negatively-charged outer
electron becomes weaker, which is why the outer electron is more easily lost.
Fluorine (Group 7) - Fluorine atoms have nine electrons. Two of these fit into the first shell, and
the remaining seven electrons fit into the second shell. The atoms of the elements in Group 7 (also
called the halogens) have seven electrons in their highest occupied energy level (the outer shell).
This is why their chemical properties are similar.…read more

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Conductive when liquid - ions are charged particles, but ionic compounds can only conduct electricity if their ions
are free to move. So ionic compounds do not conduct electricity when they are solid, but they do conduct
electricity when they are dissolved in water or when they are melted.…read more

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