Lesson 2 Atomic Structure & Chemical Reactions (PDF)

Atomic Structure and Chemical Reactions Lesson 2 + Li Medicine (Pathway Programme) Chemistry Module - Ms Solav Salih F  Learning Points Understand Describe the key Explain differ...

Atomic Structure and Chemical Reactions Lesson 2 + Li Medicine (Pathway Programme) Chemistry Module - Ms Solav Salih F  Learning Points Understand Describe the key Explain different different types of features of the types of chemical chemical reactions subatomic particles bonds and their and how to balance and isotopes properties a chemical equation Lesson 1 recap.. Atoms as solid, Discovery of Atoms are Electrons orbit Location of indivisible electrons, mostly empty the nucleus in electrons spheres. suggesting atoms space with a fixed paths. described as contain smaller dense nucleus. ‘clouds’ around particles. the nucleus  Modern Atomic Structure An atom is composed of three subatomic particles: Proton: Positively charged Located in the nucleus Relative weight of 1 Neutron: Neutral (no charge) Located in the nucleus Relative weight of 1 Electron Negatively charged Located in shells (or energy levels) around the nucleus Relative weight of 0 (negligible weight)  What are isotopes? Isotopes are atoms of the same element with (No. of protons) different numbers of neutrons (But the same number of protons). They have nearly identical chemical properties, (protons+neutrons) but different physical properties The relative atomic mass of an element in the periodic table is the weighted average of the masses of the atoms of the isotopes. Relative atomic mass takes into account the abundance of each of the isotopes of the element. relative atomic mass = (12x0.99) + (13x0.01) Calculating the Relative Atomic Mass Question Answer Copper has two isotopes: Copper-63 which accounts for 69% of copper (69 X 63) + (31 X 65) Copper-65 which accounts for 31% of = 6362 copper Calculate the relative atomic mass of 6362 / 100 = 63.6 copper to one decimal place. Radioactivity The phenomenon in which the nuclei of unstable atoms are emitting invisible rays or radiation to give more stable elements. In medicine, radiation is used to diagnose illnesses, and in high doses to treat diseases such as cancer  Understanding Chemical Reactions In a chemical reaction, bonds between atoms in the reactants are broken, and atoms rearrange and form new bonds to make the products. No atoms are created or destroyed — law of conservation of mass That is why, chemical equations need to be balanced The chemical formula of compounds are used in equations, with little subscript numbers indicating the number of atoms of those elements in the compound, and big coefficient numbers indicating the number of molecules. O O H H H H O O H H H H  1. Synthesis 2. Decomposition reactions reaction A type of chemical reaction in A type of chemical reaction in which two or more substances which a compound breaks down combine to form a more complex into two or more compounds product.  3. Single 4. Double replacement replacement A chemical reaction in which A reaction in which the metals in one element replaces another in two ionic compounds exchange a compound. partners. Real-World Chemical Reactions Precipitate Combustion reactions reactions Two solutions of soluble salts are Exothermic reactions, in which mixed resulting in an insoluble Oxygen combines with a solid (precipitate) forming. compound to form carbon dioxide and water.  Balancing equations 1. How many atoms are there in total in a molecule of CaCO ? 2. Balance the chemical equation so there are equal numbers of atoms on both sides. 3. What type of reaction is the above reaction?  Forces Driving Chemical Bonding Metals Non-metals Metals can be found in the middle Non-metals can be found on the right and on the left hand side of the hand side of the periodic table. periodic table. Ionic bonds form between metals and non-metals. Covalent bonds form in most non-metal elements Only metal elements are involved in metallic bonding.  Li F What are ionic bonds? An ionic bond is formed when a metal and non-metal react. Metal atoms become positively charged ions by losing electrons. Non-metal atoms become negatively charged ions by gaining electrons. The oppositely charged ions are very strongly attracted to each other. This is known as an electrostatic attraction.  2+ 2- Mg Handy O tips For elements in groups 1,2 and For elements in groups 6 and 7, 3, the number of electrons lost the number of electrons gained is the same as the group is 8 subtract the group number number (e.g. magnesium is in (e.g. oxygen is in group 6 and group 2 and forms a 2+ ion). forms a 2- ion).  Ionic bond properties + - + An ionic compound is composed of an ionic lattice, which is a repeating pattern of - + - oppositely charged ions held together by strong electrostatic attractions. + - + A lot of energy is required to overcome these strong attractions, hence the high melting and boiling points. They can conduct electricity when they are either melted or dissolved in water to form an aqueous solution  H H What are covalent bonds? A covalent bond is formed when two atoms share a pair of electrons to achieve stability. The electrons which contribute towards a covalent bond are found in the outer shells of the atoms. Usually each atom contributes one electron, but some atoms can react to make multiple covalent bonds.  He Ne Electron Rules Recap Two electrons can Eight electrons can occupy the first shell. occupy the other shells. The shells must be filled in order of closest to the nucleus, to furthest from the nucleus. When reacting, the aim is for an atom to achieve a full outer shell. F F This means the desired electron configuration is the same as a noble gas e.g. like helium and neon shown to the left.  Covalent bond properties Simple covalent substances can not conduct electricity. This is because covalent bonds are fixed and the electrons can not move. Covalent bonds are very strong but there are Cl Cl weak intermolecular forces between molecules which do not require a lot of thermal energy to be overcome. This means that simple covalent Cl Cl substance have low melting points and are often liquid or gas at room temperature. Cl Cl  + + + + + + + + + + + + + + + + + + What is metallic bonding? Metals exist in giant repeating structures of positive metal ions surrounded by electrons which have delocalized from the outer electron shells. Strong electrostatic forces exist between the positive metal ions and the delocalized electrons.  Metallic bond properties Metals are good conductors of electricity and heat. Metals have high melting and boiling points.. The strong electrostatic forces between the positive ions and delocalized electrons requires a high amount of energy to overcome. Most pure metals are malleable, which means that they can be bent or hammered into place. The + + + + + regular structure allows the layers to slide over each other upon impact. + + + + + Most metals are lustrous (shiny), due to the delocalized electrons on the surface of a metal. + + + + +  End of Lesson 2 Thank you for listening