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iGCSE Chemistry: Simple molecules & covalent bonding - core

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What is meant by the term atom?
An atom is the smallest part of an element
What is meant by the term molecule?
A molecule is made of a fixed number of two or more atoms covalently bonded together
What is the total number of atoms in the formula Be(OH)₂ ?
5
Explain why atoms are neutral
The numbers of electrons and protons are equal
State the mass and charge of a neutron
Neutron: mass=1, charge =0
State the mass and charge of a proton
Proton: mass=1, charge=+1
State the mass and charge of an electron
Electron: mass=almost zero, charge=-1
State the particle that is found in the shells orbiting the nucleus
Electrons
State the particles that are found within the nucleus of an atom
Protons and neutrons
How many neutrons in a typical atom of fluorine?
10
How many protons in a fluorine atom?
9
Tritium, an isotope of hydrogen, has a mass number of 3. How many neutrons does an atom of tritium contain?
2
What are isotopes?
Isotopes are atoms of the same element (same number of protons) but with a different number of neutrons (different mass)
What is a mass number?
Mass number is the number of protons plus the number of neutrons in an atom
What is an atomic number?
The atomic number is the number of protons in an atom
What is meant by the term relative atomic mass, Aᵣ?
The average mass of an atom of an element, relative to 1/12th of the mass of an atom of carbon-12
What is the atomic number of a chlorine atom?
17
What is the relative atomic mass (Aᵣ) of a potassium atom?
39
How are elements arranged in the periodic table?
in order by atomic number
On the Periodic table what is the meaning of the word Group?
A Group is a vertical column of similar elements
On the Periodic Table what is the meaning of the word Period?
A Period is a horizontal row of elements
How many electron shells do the elements in the third period have?
3
How many electrons can the first, second and third shells hold?
First 2, second 8, third 8
How many electrons in a calcium atom?
20
How many electrons in the outer shell of group 7 elements?
7
Write the electronic configuration of potassium
2,8,8,1
Where are non-metals found on the periodic table?
At the top right, plus hydrogen
On the Periodic table what is the meaning of the word Group? What does that tell us about the electron configuration of the atom?
same number of electrons in the outer shell
On the Periodic Table what is the meaning of the word Period? What does that tell us about the electron configuration of the atom?
same number of electron shells
Why do elements in the same group of the periodic table have similar chemical properties?
Elements in the same group of the periodic table have the same number of electrons in their outer shell
Explain, in terms of the arrangement of electrons in its atoms, why neon is very unreactive
Neon has 8 electrons in the outer shell, so it is full. Therefore it does not easily gain or lose electrons
What are the elements in group 0 called?
Noble gases
What is special about the elements in group 0?
They are very unreactive (because they have full outer electron shells)
Describe the formation of a covalent bond
The sharing of a pair of electrons between two nuclei
Give the definition of a covalent bond
Strong electrostatic attraction between a shared pair of electrons and two nuclei
Draw a dot and cross diagram to show the covalent bonding in a molecule of ammonia, NH₃
Draw a dot and cross diagram to show the covalent bonding in a molecule of carbon dioxide, CO₂
Draw a dot and cross diagram to show the covalent bonding in a molecule of chlorine, Cl₂
Draw a dot and cross diagram to show the covalent bonding in a molecule of hydrogen chloride, HCl
Draw a dot and cross diagram to show the covalent bonding in a molecule of hydrogen, H₂
Draw a dot and cross diagram to show the covalent bonding in a molecule of methane, CH₄
Draw a dot and cross diagram to show the covalent bonding in a molecule of nitrogen, N₂
Draw a dot and cross diagram to show the covalent bonding in a molecule of oxygen, O₂
Draw a dot and cross diagram to show the covalent bonding in a molecule of water, H₂O
Explain why carbon dioxide gas, CO₂, is a gas at room temperature
Carbon dioxide has a simple molecular structure with weak intermolecular forces that require little energy to overcome
Explain why methane gas, CH₄, is a gas at room temperature
Methane has a simple molecular structure with weak intermolecular forces that require little energy to overcome
If a substance has a simple molecular structure, what physical state might it be at room temperature?
Gas or liquid (low melting point)
Why is the boiling point of a larger molecule higher than that of a smaller molecule?
Larger molecules have more attractions between them which must be overcome when a substance boils
A gas is bubbled through limewater and the limewater goes cloudy. Identify the gas.
Carbon dioxide
Describe the test for ammonia gas
Turns damp red litmus paper blue
Describe the test for carbon dioxide gas
Bubble the gas through limewater and see if it goes cloudy
Describe the test for chlorine gas
Turns moist litmus paper white (bleaches)
Describe the test for hydrogen gas
Use a lit splint to see if the gas pops
Describe the test for oxygen gas
Use a glowing splint and see if it relights
In the test of a gas, a glowing splint relights. What is the gas?
Oxygen
In the test of a gas, a lit splint gives a squeaky pop. What is the gas?
Hydrogen
Which gas will bleach moist litmum paper?
Chlorine
Which gas will turn damp red litmus paper blue?
Ammonia
Describe the chemical test for water
Add water to anhydrous copper(II) sulfate which will change from white to blue if water is present