[note][sru] Diversity 1.3 Covalent Bonding 2024

1 D 1.3 Covalent Bonding CHIJ ST. NICHOLAS GIRLS’ SCHOOL Sec 2 Science 2024 Diversity D 1. Exploring Diversity of Matter by their Physical Properties D 1.3 Covalent Bonding (a) Describe the formation of a covalent molecule by the sharing of a pair of electrons in order to obtain electronic configuration of a noble gas. (b) Describe the formation of covalent bonds between two non -metallic elements. Eg. HCl, CO 2 and CH4, using ‘dot and cross’ diagrams to illustrate (c) Deduce the arrangement of electrons in other covalent molecules (d) Relate the physical properties (including electrical property) of covalent substances to their structure and bonding (e) State the number and types of atoms of each element from a given chemical formula of a substance ; highlight the various categories ; simple ions, polyatomic ions, prefixes such as mono-, di-, tri-

2 D 1.3 Covalent Bonding (A) Covalent Bonding between two atoms of the same non-metallic element Covalent bonds: https://www.youtube.com/watch?v=LkAykOv1foc Example 1: Covalent bonding between hydrogen atoms ______ pair of electrons shared gives rise to ________________________ Example 2: Covalent bonding between oxygen atoms There are _____ pairs of electrons shared; hence it is a __________ covalent bond. Molecular Formula: _________ (__________ molecule) Structural Formula: _________ Example 3: Covalent bonding between nitrogen atoms There are ____ pairs of electrons shared; hence it is a __________ covalent bond. Molecular Formula: _________ (diatomic molecule) Structural Formula: _________ Electrons of both hydrogen atoms will be shared. Covalent bond is formed when atoms of non -metallic elements _______ electrons so as to achieve the stable electronic configuration of a noble gas to form molecules. Definition of covalent bond: It is electrostatic forces of __________ between the 2 positively-charged _______ and the pair of negatively-charged __________ they _____________.

3 D 1.3 Covalent Bonding The above elements exist as diatomic molecules. The structural diagrams and chemical formulae of the diatomic molecules are given below. Hydrogen & Group VII elements (X2) Oxygen (O2) Nitrogen (N2) Non-metallic element Chemical symbol Molecular formula of the molecule Structural formula Hydrogen H Fluorine F Chlorine Cl Bromine Br Iodine I Oxygen O Nitrogen N Conclusions: 1. Two _________ of the _________________ may share electrons to achieve stable full valence shell electron configuration. 2. The atoms held together by sharing electrons is called a ____________. 3. The ___________ of electrons the two atoms ___________ is determined by the no of electrons each atom _________ to complete its valence shell. 4. All non-metallic elements exist as __________ except for noble gases. 5. Therefore, hydrogen exists as ______________, _________. oxygen exists as ____________, _______ and etc. But, helium exists as ______________ neon as ____________ and etc X - X

4 D 1.3 Covalent Bonding (B) Covalent Bonding between atoms of different non-metallic elements to form compounds Example 1: Covalent bonding between hydrogen atom and chlorine atom Chemical name : ________________ Molecular Formula: __________ Structural formula: _____________( __________________) Example 2: Covalent bonding between hydrogen atom and oxygen atoms Molecular Formula: __________ Structural formula: ____________(_____________________) Points to note when drawing dot-and-cross diagram for covalent molecules 1. Use dots and crosses to represent electrons of different elements 2. Include the atomic symbols of the elements 3. Make sure that all the atoms in the substances drawn have fully-filled valence shells 4. Make sure that each atom retains its original number of electrons – no “missing” or “extra” electrons except the ones being shared 5. Make sure electrons are shared in pairs.

5 D 1.3 Covalent Bonding Practice Draw the dot-and-cross diagrams to show how the electrons are arranged in the following substances, showing only the valence electrons: (answers in power point slides) (a) CO2 (b) NH3 (c) CH4 (d) H2O2 (e) CHFClBr (f) CH3OH (More practice qns on the power point slides)

6 D 1.3 Covalent Bonding Names and Chemical Formulae of Covalent molecules (compounds) In some cases, the names of covalent compounds have prefixes (starters) that tell you how many of each element is required in the formula. o Prefixes: Mono – 1 Di – 2 Tri – 3 Tetra – 4 Name Formula Name Formula CO HCl CO2 H2S SO2 NH3 SO3 CH4 NCl3 CCl4 H2O True or false ? 1, Molecules are made up of two or more atoms sharing electrons. _________ 2. There are both molecules of elements and molecules of compounds. _________ 3. Sodium chloride is made up of molecules. ________ STEM Activities You are to research on the following molecules and share one thing about how these molecules relevant in everyday life. 1. Hydrogen chloride 2. Carbon dioxide 3. Hydrogen sulfide 4. Sulfur dioxide 5. methane 6. ammonia

7 D 1.3 Covalent Bonding Structures of Covalent Substances Covalent substances may have 2 different types of structures with different properties – Simple molecular structure – Giant molecular structure (will be covered in Secondary 3) Simple Molecular Structure • Most non-metallic __________ and their ____________are made up of _________________, e.g. hydrogen (H2), oxygen(O2), bromine(Br2) , water(H2O) , carbon dioxide (CO2) and etc. • These substances exist as individual simple molecules and have _____________________________________. • Within the molecule, the atoms are bonded by ____________ bonds which is a _________- bond. • However, between them, the small molecules are held loosely together by ____________________________________. H Cl H H Cl Cl Weak intermolecular forces between molecules Strong covalent bonds between atoms

8 D 1.3 Covalent Bonding The significance of the intermolecular forces: • The strength of the intermolecular forces directly affects the amount of energy needed to melt or boil the substance. And since intermolecular forces are generally ___________, boiling points of substances made up of simple molecules are generally _________. • In general however, the greater the ________ of the covalent molecules, the ________ the intermolecular forces and _________ energy required to overcome it in order to boil or melt the covalent substance. • For examples: substance molecular formula Mr (sum of Ar) boiling point/°C hydrogen –253 nitrogen –196 oxygen –183 Methane CH4 -161 ethane C2H6 -89 Propane C3H8 -42 Note: The __________ bonds within the molecule are _____________ during the process of melting and boiling, The ________________ remain unbroken and merely ____________ from each other. The covalent bonds would only be broken during chemical reactions, not during physical change.

9 D 1.3 Covalent Bonding Physical properties of substances with Simple Molecular Structure Property Explanation Melting and boiling point • ______ melting and boiling points (Many of these substances are gases or volatile at room temperature, e.g. CO2, H2, N2, CH4 etc. ) • These substances (elements or compound) have covalent