Year 10 Science Chemical Reactions - Physical & Chemical Changes PDF

Year 10 Science Chemical Reactions Physical & Chemical Changes St Michael’s Collegiate LDE  Recap - Ion = charged atom Cation = positive ion Anion = negative ion Formed when a neutral atom LOSES Forme...

Year 10 Science Chemical Reactions Physical & Chemical Changes St Michael’s Collegiate LDE  Recap - Ion = charged atom Cation = positive ion Anion = negative ion Formed when a neutral atom LOSES Formed when a neutral atom GAINS electrons electrons = More protons than electrons = Less protons than electrons Come from metallic atoms (columns 1 Come from non-metallic atoms (part & 2, and some transition metals of of columns 15, 16 & 17 of periodic periodic table; Hydrogen is non- table) metallic cation)  A sodium atom has 11 protons Cations in the nucleus and so has a charge of +11 in the nucleus. As an atom it also has 11 electrons each with charge -1. Na To achieve a lower energy state, Na will tend to lose its and will then valence have: electron 11 protons … +11 10 electrons … -10 Ion charge Anions A sulfur atom has 16 protons in the nucleus and so has a charge of +16 in the nucleus. As an atom it also has 16 electrons each with charge -1. To achieve a lower energy S state, Sulfur will tend to gain two electrons to fill it’s valence shell and will then have: 16 protons … +16 18 electrons … -18 Ion charge -  Types of bond In an ionic bond, atoms transfer electrons and become ions Atoms share electrons in a covalent bond  Ionic Bonds The S2- anion will be attracted to the two sodium Na + cations. This exchange of electrons is a chemical reaction. An ionic bond is formed between oppositely charged ions. The ionic compound formed, has equation Na2S Is called sodium sulfide. This electron exchange only occurs between metal and  Formula & name of ionic compounds Formula: Cation symbol first, then Anion symbol. If more than one atom is needed, put the necessary number at the bottom right corner (e.g., Na2) 1. Cation (metal): name is the same as the atom 2. Anion (non-metal): name is changed to end by –ide For example, bromine and calcium react to form a compound of: Formula: CaBr2 Name: calcium bromide Ionic Bonds (Bohr diagram) More examples of Ionic Bonds (Bohr diagram) MgCl2 More examples of Ionic Bonds (Lewis diagram) Sodium chloride Potassium sulfide Scandium fluoride  Ionic compounds properties Overall number of p+ and e- are equal in ionic compound e.g., NaCl Na ion: 11 p+ and Cl ion: 17 p+ = 28 + charges Na ion: 10 e- and Cl ion: 18 e- = 28 - charges Ionic compound arranged in 3D lattice (regular arrangement of ions) So, the strong force of attraction between oppositely charged ions means that ionic compounds have high melting and boiling points  Physical & Chemical Physical change: Changes Physical properties of substance may change (appearance) BUT NO new substance is formed Change in shape or form (e.g., Solute crushing aluminium can) can be Expansion or contraction visible again by (temperature of a substance evaporati increases or decreases, leading to on increase or decrease in volume) Change of state (solid, liquid, gas) Mixing substances together (e.g., solution) Often reversible Chemical change: Physical & Chemical Change that results in a NEW substance being Changes formed New substance formed can be solid, liquid, gas Hard to reverse Detect change by: permanent colour change gas emitted (smell) or bubbles formed formation of precipitate (new solid formed in clear solution) energy is produced (exothermic reaction) or  Complications? Painting Mixing Burning of sugars Cutting metal Spilling milk Unquestionabl Chemical Physical Unquestiona y but … but … bly Physical or Chemical Change? Physical or Chemical Change? Physical or Chemical Change? May need some research!