Lesson 1 : Structure of Animal and Plant Cells

It is important that you know the structure of animal and plant cells and are able to label the different parts. It is a favourite with examiners to have diagrams of cells requiring labelling in exams.

Task 1: from memory label the cells below and write in the function

Check your answers:

There are many similarities and differences between animal and plant cells. Make sure you know these. Similarities Differences

1. Have a nucleus 1. Plant cells have a cellulose cell wall

2. Have a cytoplasm 2. Plant cells have a vacuole containing cell sap

3. Have a cell 3. Plant cells have chloroplast membrane

4. Contain 4. Many plant cells have a box-like shape whilst animal cell shape varies mitochondria

5. Plant cells have the nucleus to the side of the cell, animal cells have a nucleus in 5. Contain ribosomes the middle

Task 2: Complete the sentences by filling in the gaps.

Both plant and animal cells contain a nucleus. This holds genetic information. Both animal and plant cells have a cell membrane. This controls what enters and leaves the cell. Only a plant cell contains chloroplasts. This is where photosynthesis happens. Both cells contain mitochondria. This is where respiration occurs.

Check your answers:

Lesson 2: The movement of substances

Water is the main component of all cells. We find water in the cytoplasm and in cell sap. This water contains many dissolved substances and these substances plus the water enter and leave the cells through the cell membrane. The cell membrane allows certain particles through it but it blocks the passage of others. Because of this nature it is described as a partially (or selectively) permeable membrane. Particles enter and leave cells by three processes: 1. Diffusion 2. Osmosis 3. Active transport

Task 1: Read the following and highlight the key words.

Diffusion Particles in liquids and gases have kinetic energy, therefore they move about at speed in all directions. These particles move in a random motion. Where there is an area of high concentration some of these particles collide into one another, lose energy and slow down. Others will escape from the area of high concentration to an area of low concentration elsewhere. Very few particles travel the opposite way. The result is a concentration gradient with particles diffusing from an area of high concentration to an area of low concentration. Diffusion occurs in gases and with any substance in a solution.

Task 2: Write down the definition for diffusion. ______

The speed particles diffuse across the cell member depends on; temperature, surface area and the concentration gradient.

Task 3: Complete the table below.

Answers: Diffusion is the movement of particles from an area of high concentration to an area of low concentration across a partially permeable membrane.

Steepest Fastest

Fairly fast Fairly steep

Steep Fast

Low Slow

Lesson 4: Structure of an Atom

All matter is composed of atoms. An atom is composed of 3 types of sub-atomic particles:

1. Protons 2. Neutrons 3. Electrons The protons and neutrons are present in the centre of an atom, forming a small nucleus. The electrons orbit around the nucleus in shells or energy levels.

Task 1: Label the structure below.

2) 3)

5) 4)

Calculating sub-atomic particles from atomic number and mass number

Task 2: read and make notes on how to calculate the number of protons, neutrons and electrons.

We can calculate the number of sub-atomic particles (i.e. electrons, protons, neutrons) if the atomic mass or atomic number is provided for an element. Similarly, the atomic number and mass number can be calculated for any element if the number of subatomic particles is known.

From the definitions of Atomic number and Atomic mass, we know:

Atomic number = the number of protons Mass number = the number of protons + the number of neutrons

From these, we can deduct:

Number of neutrons = Mass number – Atomic number

Atom has no overall charge, which means the there are equal number of negatively charged electrons and positively charged protons. If we know the number of protons (or atomic number) of an atom, this will be equal to the number of electrons of that atom. Number of electrons = Number of protons

Task 3: writing down the following for lithium.

Number of protons = Number of electrons = Number of neutrons =

Answers. Task 1; 1= nucleus, 2 = shells, 3 = electron, 4 = neutron, 5 = proton

Task 3; Protons = 3, electrons = 3, neutrons = 4

Task 4: complete the table below.

Element Proton number Electron number Neutron number Carbon Nitrogen Oxygen

Answers task 4:

Element Proton number Electron number Neutron number Carbon 6 6 12-6 =6 Nitrogen 7 7 14-7 = 7 Oxygen 8 8 16- 8 = 8

Lesson 5 Atomic structure diagram

The atomic structure is drawn with the nucleus in the center, and electrons arranged outside in circles called energy levels or shells. The electrons in an atom occupy the innermost available shells, i.e. the lowest available energy levels.

The innermost shell, or the first shell, can hold only 2 electrons. The second and third shells can hold up to 8 electrons each.

The above diagram shows the electron configuration for Argon. It has the electron structure of 2,8,8

Task 1; complete the sheet below.

Answers

Lesson 6 Isotopes

All the atoms of a particular element have the same number of protons. This proton number or atomic number determines the chemical properties of an atom. However, the number of neutrons may vary within the atoms of an element.

Atoms of the same element that have the same number of protons but different number of neutrons are called isotopes of that element.

Or in other words,

Atoms of the same element with the same atomic number but different atomic masses are called isotopes of that element.

Task 1: write your own definition of an isotope

Example

The atomic number of carbon is 6. All carbon atoms have the same atomic number, but their mass number might differ because of different number of neutrons.

Most of the carbon atoms contain 6 protons and 6 neutrons, and has a mass number 12. However, some carbon atoms also exist with 6 protons and 8 neutrons, which gives it a mass number 14.

12C and 14C are isotopes of carbon.

Comparison of two isotopes of carbon

Electrons 6 6 Same

Protons 6 6 Same

Neutrons 6 8 Different

Atomic number 6 6 Same

Mass number 12 14 Different

Task 2: complete the table below. Number of Number of Number of Name Atomic Mass Protons neutrons Electrons

Hydrogen-2 2 1 1 1

Hydrogen - 3

Magnesium-24 24 12 12

Magnesium-25 25 12 12

Carbon-12 6 6

Carbon-13 6 6

Carbon-14 6 6

Answers:

Number of Number of Number of Name Atomic Mass Protons neutrons Electrons

Hydrogen-2 2 1 1 1

Hydrogen - 3 3 1 2 1

Magnesium-24 24 12 12 12

Magnesium-25 25 12 13 12

Carbon-12 12 6 6 6

Carbon-13 13 6 7 6

Carbon-14 14 6 8 6

Lesson 7 The Periodic table

The modern periodic table has all the elements arranged in strict order of their atomic numbers and therefore can be seen as an arrangement of the elements in terms of their electronic structures.

All the elements are placed in order of increasing atomic number in horizontal rows called periods. Arranging the elements in order of their proton numbers gives repeating patterns in the properties of elements. Elements with similar properties are placed in the same vertical column, called groups.

Task 1: make notes on how the groups are arranged Groups

The vertical columns of the periodic table are called groups. There are eight groups in total. The groups are numbered from 1 to 7 going from left to right, and the eighth group on the right is Group 0.

Elements in the same group have the same number of electrons in their highest energy level (outer shell) and this gives them similar chemical properties.

The elements in Group 1 have only one electron in their outer energy level or shell. Similarly, atoms with two outer shell electrons are placed in Group 2.

Some of the groups have their specific names:

Group 1: The alkali metals. Group 2: The alkaline earth metals. Group 7: The halogens. Group 0: The noble gases.

Task 2; make notes on how the period are arranged.

Periods

The horizontal rows are called periods. The Periods represent the energy shell these atoms outer electrons are located within. It means that all Period 2 elements have their outer electrons in the second energy level or shell; Period 3 elements all have their outer electrons in the third energy level/shell, and so on.

So…. If an element has the electron arrangement of 2,8,1 we know it is group 1 AND period 3.

2,8,1 (Ends in a 1 = group 1)

(3 numbers for 3 shells = period 3)

Lesson 8 Group 1 – Alkali Metals

The Group 1 elements are placed in the vertical column on the left-hand side of the periodic table. Group 1 elements form alkaline solutions when they react with water, which is why they are called alkali metals. Lithium, sodium and potassium all belong to alkali metals. All Group 1 elements have 1 electron in their outer shell.

Task 1: read and summarise the physical properties of Alkali metals.

Alkali Metals have lower melting and boiling Points

All Group 1 elements have one electron in their outermost shell which is held very weakly by the nucleus. This electron can drift further from the nucleus than in most atoms of other elements. This results in Group 1 elements having larger atomic radii than those elements that follow them in their respective periods. The large atomic size results in weaker forces between neighbouring atoms. It is these weaker attractive forces due to the large atomic radii between neighbouring atoms of Group 1 elements that result in lower melting and boiling points when compared to other metals.

The decrease in melting and boiling points down the group can be explained by the additional shell being added to the previous element causing the atomic radius to increase. The increasing atomic radius means weaker forces between the atoms and so a lower melting and boiling point.

Alkali Metals are soft

Alkali metals are soft metals that can be cut with a knife and silvery coloured. Freshly cut alkali metals are shiny but tarnish rapidly due to reaction with oxygen in the air. They are generally stored under oil.

It is the reduced interatomic forces in these elements that make them relatively soft.

Alkali metals are extremely good conductors of electricity and heat

Alkali metals have one electron in their outermost shell which is held very weakly by the nucleus. The outer electron can drift further from the nucleus and move relatively freely. On the application of an electric field the large numbers of free flowing electrons in the outer shells conduct electricity through the metal.

Similarly, on the application of heat the free moving electrons in the outermost shells gain a lot of energy and transfer this through the metal via collisions with the other free moving electrons.

Alkali metals have low density

Lithium, sodium and potassium are less dense than water and therefore can float on water. Rubidium and caesium are denser than water.

Summary:

Task 2: Read and summarise the chemical properties of alkali metals

Chemical Properties of Alkali Metals

The alkali metals are the most reactive group of metals in the Periodic Table. They contain one weakly held electron in their outer shell which is readily transferred in chemical reactions.

Reactions of alkali metals with water

All the Group 1 elements react vigorously with cold water. They react with water to form hydrogen gas and an alkaline solution of the metal hydroxide. All the Group 1 elements readily give up their weakly held outermost electron resulting in a positive metal ion with a full outer shell i.e. the stable electronic arrangement of a noble gas. In a reaction, an atom of a Group 1 element loses one electron and forms an ion with a single positive charge. The process of losing an electron is termed as oxidation.

Summary:

Explaining trends in reactivity

The reactivity of Group 1 elements increases going down the group. This is because on going down the group:

• The atoms get larger. The atomic radii increase with atomic number down the group. Each succeeding element has its electron in one more shell than the previous element. • The outer electron gets further away from the influence of the nucleus. Therefore, the attractive force between the nucleus and the electron gets weaker and so the electron is more easily given up.

Lithium (Li) Sodium (Na) Potassium (K)

2.1 2.8.1 2.8.8.1

Potassium is more reactive than lithium although they both need to lose only one electron to have full outer shells. This is because the outer electron of potassium atom is further from the positive attractions of the nucleus compared to the outer electron of lithium. Therefore, it is easier for potassium to lose its outer electron.

Task 3: 6 mark exam question on explaining the trend in group 1 as you move down from lithium to potassium.

Answer: As you move down group 1 the reactivity increases. This is due to the atom getting larger as you move down the group. This means the outer electron is further away from the positive attraction from the nucleus. This means the electron is easier lost and the reaction is more violent.