Core Chem Unit 1-2

What is an element?

A substance that consists of only one type of atom

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What is an isotope?

An isotope is a different form of the same element - it has the same number of protons and electrons but different numbers of neutrons

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How do you calculate the Ar (average/relative atomic mass) using isotopes?

Ar = (isotope abundance x isotope mass number) / (sum of abundances of all isotopes)

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Who is responsible for coming up with the plum pudding model?

JJ Thomson - discovered electrons and theorised the plum pudding idea

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After which experiment did Bohr then create the nuclear model?

Rutherford's experiment which discovered that atoms are not balls of positive charge

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How many electrons are allowed in each of the first three shells?

2, 8, 8

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How did Mendeleev arrange the elements to create the Periodic Table?

...he put elements mainly in order of atomic mass (Ar) but ensured that elements with similar properties were grouped

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Why did Mendeleev leave gaps in his table?

...he left gaps to make sure that the patterns he spotted still worked, and predicted that other elements were yet to be discovered and would fill the gaps

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What did the discovery of isotopes mean for Mendeleev's periodic table?

the discovery of isotopes meant that he was correct not to order elements only based on their Ar

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If iodine generally reacts by forming negative ions, then is it a metal or a non-metal?

Metals form positive ions mostly, so iodine is a non-metal

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State three properties of metals

strong, malleable, high melting/boiling points, good heat and electricity conductors, some are ductile

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What are the products of any group one element reaction with water? with chlorine? with oxygen?

with water: produces hydrogen gas, with chlorine: salt, with oxygen: oxide

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Why do group 7 elements get less reactive as you move down the group (fluorine to iodine)?

...they get less reactive because they have more and more shells, which make it more difficult (takes more energy) to gain an electron

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why are group 0 elements so unreactive? What is the word for them?

Group 0 elements are the noble gases which are inert (unreactive) because they have full outer electron shells and are therefore stable

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State three trends as you go down group 1

As you go down: reactivity increases; melting points decrease; the atomic mass is higher (more shells too)

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What happens to the boiling/melting points of halogens as you move down the group?

Group 7: as you move down the bp/mp increases

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What is the trend in boiling point as you go down group 0?

As you go down the noble gases, the boiling point increases due to more electrons and therefore more intermolecular forces to overcome (more energy required to break them)

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State the three types of bonding and what types of atom/element they occur between

Ionic = metal + non-metal Covalent = non-metal + non-metal Metallic = metal + metal

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State three properties of ionic compounds

Ionic compounds... have high boiling points because the forces are strong between ions; can conduct electricity when molten; dissolve easily in water and are able to carry a current in solution

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Describe the structure of an ionic compound

Ionic compounds form giant ionic lattices which are the positive and negative ions attracted to each other in regular arrangement

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What are the properties of simple molecular substances?

they are often covalently bonded and so have weak intermolecular forces - this means the boiling point is low. Little energy is required to change their state so they are often gases at room temp. No charge means cannot conduct.

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Give three common examples of simple molecular substances

Any Three From: Hydrogen (H2), Chlorine (Cl2), Oxygen (O2), Nitrogen (N2), Methane (CH4), Water (H2O), Hydrogen Chloride (HCl)

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True or False: giant covalent structures have low boiling points

FALSE: Giant covalent structures actually have very high boiling points because all atoms are bonded to each other by strong covalent bonds

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Give three properties of graphite, and he type of structure that it is

Graphite is an allotrope of carbon (covalent bonds). Properties include: high melting point, conductor or thermal and electricity, a soft material

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Describe the structure of a metallically bonded compound

Metallic bonding produces compounds which have giant structures of positive ions surrounded by a 'sea' of delocalised electrons which are free to move. There are strong forces of attraction between the + ions and electrons.

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Core Chem Unit 1-2

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