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This document has summaries on the various topics of agricultural sciences in grade 11
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Grade 11 Notes Agricultural sciences By E.C. Mabuza
Topic 1: Basic chemistry What is chemistry? Chemistry is the study of the properties, composition and structure of matter, the changes that occur in matter, and the energy that is released during these changes.
Matter - Is anything that can occupy space and has mass (it weighs something) and volume (it take up space) Atom - is the smallest unit of matter that cannot be broken down by chemical means They are made up of the following sub-atomic particle; neutron , proton and electron Proton- is a subatomic particle with a positive charge Neutron - is a subatomic particle with no charge Electron - is a subatomic particle with a negative charge Valence electron - is the electron in the outer shell of an atom It is determined by the main group number of an element found in its column in a periodic table e .g Carbon is in group 4 and has 4 valence electron Atomic number - number of protons in the nucleus of an atom Atomic mass number - number of protons and neutrons in the nucleus of an atom Element - is a substance that cannot be broken down into simpler substance by chemical means (element adhere to form a molecule) Molecule - is a group of two or more atoms which are bond together to form a compound (molecule can be broken down chemically into elements they made up of) e .g water molecule (H 2 O) is made up of two hydrogen atom and one oxygen atom carbon dioxide (CO 2 ) is made up of 1 carbon atom and two oxygen atom Compound - substance that result from a combination of two or more different elements Periodic table - is the table of all the known elements arranged in order of their atomic number Isotopes - element that has equal number of proton but different number of neutrons
Interpreting a periodic table Periodic table groups Groups in a periodic table are numbered 1- 18 from left to right Group 1 : made up of alkali metals (note: hydrogen is not considered a metal) Alkali metals are very reactive (most reactive group in the periodic table) They react violently with water Has one valence electron Group 2 : made up of alkali earth metals alkali earth metals are very reactive, but less reactive than alkali metal Has two valence electron Differences between alkali metals and alkali earth metals Alkali metal: have one electron in their outermost shell Alkaline earth metal: has two outer shell electrons Similarities between alkali metals and alkaline earth metals They are both good electrical and heat conductors They are the most reactive metals in the periodic table They have low melting point compared to other metals
Group 3 - 12 : made up of transition metals (they contain metals) Some transitional metals are below the main table (they contain Lanthanide and Actinide series ) Lanthanide : They follow transitional metal atomic number 57 in period 6 of the periodic table Has 3 valence electron They are very reactive Actinide : They follow transitional metal atomic number 89 in period 7 of the periodic table Has 3-6 valence electron They are radioactive Most can be produced in laboratories Group 13 : Boron group (made up of other metals) Has 3 valence electron They are highly reactive Group 14 : Carbon group (made up of other non-metals) Has 4 valence electron Reactivity varies Group 15 : Nitrogen group (made up of other non-metals) Has 5 valence electron Reactivity varies Group 16 : made up of chalcogens (oxygen group) It is also known as oxygen family (since oxygen is first member of the family) Has 6 valence electron They are reactive Group 17 : made up of halogens They are called halogens because they give salt when they react with metals Has 7 valence electrons This are the most electronegative elements Elements in group 17 are highly reactive (because of the closeness to the noble gases. They can easily achieve the noble gas electron structure) Group 18 : made up of noble gases Have 8 valence electrons (2 for He)
Activity 3 (periodic table) 1.1 use the periodic table below to answer the following questions 1.1.1 Identify the lightest element from the periodic table (1) 1.1.2 Group 18 on the periodic table is composed of gases that are chemically inactive and cannot react with others as indicated in the periodic table grouping. Suggest the name given to this group and give TWO examples (3) 1.1.3 Copy and complete the table in your book Element Valency electrons Atomic number Mass number Magnesium Sulphur Activity 4 (periodic table) 1.1 Answer the following on a periodic table 1.1.1 Element in a periodic table are arranged in period and group. Indicate the common characteristic of element in the same: (a) Period (1) (b) Group (1) 1.1.2 Elements in group 17 and group 18 differ. Explain how the elements differ with regard to chemical reactivity (2) 1.1.3 Give a reason for the answer in QUESTION 1.2.1 (2)
Atoms can sometimes be positively charged or negatively charged. e.g H+ atom is a hydrogen atom with a positive charge. Presence or absence of hydrogen ion in a liquid determine if the liquid is acidic or basic. For an example; Tap water that we drink has ions in it, and this ion makes water either acidic or basic In our body there are small compounds called amino acids Some acids such as citric acids are found in fruits Vinegar is an acid Bicarbonate of soda is basic The pH scale Is a scale that describes how acidic or basic a liquid is. Acid- is a solution that has an excess of H+ ions. (it comes from Latin word acidus meaning sharp or sour Strong acid - acid with very low Ph. (0-4) Weak acid - acid that is partially ionised in water solution (has Ph close to 7) Base- is a solution that has an excess of OH- ions (hydroxides). (also known as alkaline) Strong base – a base that has a very high Ph. (10-14)
1.1.3 state TWO products of the chemical reaction in QUESTION 1.1. 1.2 HCL and NaOH are chemical formulae of substances used in agriculture 1.2.1 identify the chemical formulae representing the following: (a) alkine (1) (b) acid (1) 1.2.2 show the chemical reaction when HCL dissolves in water (3)
Not all atoms have same number of protons and electrons The main sub-atomic particles and their relative charge Proton: has a positive charge : They are determined by the atomic number Neutron: has a negative charge Electron: has no charge Relationship between atomic number and the number of sub-atomic particles in the nucleus The simplest element in the periodic table is hydrogen. It has atomic number 1, which means; There is just 1 proton in the nucleus of hydrogen atom To balance the positive charge of the proton, hydrogen atom has 1 negatively charged electron around the nucleus Oxygen has atomic number 8, which means; There are 8 protons in the nucleus of an oxygen atom
To balance the positive charge of the proton, oxygen atom has 8 negatively charged electron around the nucleus The number of protons + number of neutrons= atomic mass number Arrangement of electrons around the nucleus and valence Each layer in an atom can hold a certain number of electrons as follows; Closest to the nucleus: can hold only TWO electrons can exist Second shell: can hold only EIGHT electrons Third shell: can hold up to eighteen electrons Fourth shell: can hold twenty-two electron Note: the shell closest to the nucleus has lowest energy than other shells Formation of an ion An atom with one or more electron or one or more missing electron is called an ion Ions which have gained electrons are called anion (they are negatively charged) Ions that has lost one or more electron are called cations (they are positively charged) Ions of opposite charge attract one another, while ions of same charge repel one another
Activity 8 (chemical bonding) 1.1 The illustration below shows the type of chemical bonding. Answer the questions based on these ilustrations 1.1.1 Identify the type of bond shown by diagrams A and B (2) 1.1.2 Differentiate between the two types of bonds, A and B you have mentioned in QUESTION 1.1.2 (2) 1.2 analyse the following reaction and answer the questions that follows HCL + KOH KCL + H 2 O 1.2.1 Identify the chemical reaction illustrated above (1) 1.2.2 Give a reason for your answer in QUESTION 1.2.1 (1) 1.2.3 Give two chemical bonds that are involved in the above reaction and give one example of each (4) Activity 9 (chemical bonding) 1.1 The diagram below illustrates atoms responsible for the formation of a compound 1.1.1 identify the compound formed by the atoms in the diagram above 1.1.2 indicate the health benefit of the above compound 1.1.3 name the parts labelled A, B and C
Glucose: C 6 H 12 O 6 Sodium chloride: Nacl Magnesium sulphate: MgSO 4 Hydrogen: H 2 Oxygen: O 2 Ozone: O 3 Chlorine: Cl 2 Sulphur: S 8 Structural formulae Is the graphical representation of the molecular structure showing how atoms are arranged and how they are chemically bonded within the molecule. Water Lewis structure Is a diagram that show the bonding between atoms of a molecule. (You can also exclude the first 2 electrons in the inner shell when drawing a Lewis structure) Is the quickest way of showing the valence electron of an atom
Note : The main group number for an element can be found in its column on the periodic table, for an example; carbon is in group 4 and has 4 valence electron. Oxygen is in group 6 and has 8 valence electron Importance of inorganic compounds
1. Water (H 2 O) Makes up 80% of plant and animal cells Act as a cooling agent Medium for chemical reaction 2. Carbon dioxide Used by plants during photosynthesis It combines with water to form carbonic acid
Amino group : is functional group made up of a nitrogen atom joined by a single bond to two hydrogen atoms Alkanes and alcohols Differences between alkanes and alcohol Alkanes: They are made up of carbon and hydrogen atoms. The Carbon atoms are linked to each other by a single bond Alcohol: has hydroxyl group attached to the carbon atom Alkanes Basic type of alkanes, chemical formulae, structural formulae and name of alkyl group
