Chemistry 1.0 Past Paper PDF

CHEMISTRY 1.0  COMPETENCIES ▪Draw the Lewis structure of ions. ▪Apply the octet rule in the formation of molecular covalent compounds.  Ion ▪When an atom gain or lose an electron/s. ▪Cation – positively charged ion due to lose of electron making an atom has greater nu...

CHEMISTRY 1.0  COMPETENCIES ▪Draw the Lewis structure of ions. ▪Apply the octet rule in the formation of molecular covalent compounds.  Ion ▪When an atom gain or lose an electron/s. ▪Cation – positively charged ion due to lose of electron making an atom has greater number of proton. ▪Example: Mg2+ ▪Anion – negatively charge ion due to gain of electrons making an atom has greater number of electron. ▪Example: O2-  Octet Rule ▪Octet – came from the Greek word “okto” meaning “eight”. Octet configuration is the most stable arrangement an atom can have. Because of this high stability, noble gases have very little or no tendency to lose, gain, or share electrons, which happens during chemical reactions. ▪Thus, atoms that have less than eight valence electrons tend to bond with other atoms to complete the needed eight electrons in their valence shells.  Octet Rule ▪The atoms of the other elements in the periodic table tend to achieve the configuration of the nearest noble gas by reacting with the same element or with other elements to form more stable compounds.  Gilbert N. Lewis (1875-1946) ▪In 1916, Gilbert Lewis developed a system of representing the valence electrons of an atom using diagrams called Lewis's electron-dot structures or Lewis structures. ▪A Lewis structure consists of a symbol of an element surrounded by one or more dots; dots corresponds to a valence electron in an atom. Only two dots are placed in each of the four sides. ▪Example: Hydrogen Example ▪Electron configuration: 1s1 ▪Number of valence electron: 1 H ▪There are no strict rules on which sides to pair up first so the dot symbol for oxygen may be written in several equivalent forms. O O O O O (1) (2) O (3) (4) (5) (6)  Octet Rule ▪Ions may be represented using Lewis structures by simply removing (or adding) the number of dots that corresponds to the electrons lost (or gained) by the neutral atom. ▪For instance, losing the single valence electron in the neutral atom of sodium leaves a Lewis structure with no dot but with a +1 charge.  Example Element: 11Na Electron configuration: 1s2, 2s2, 2p6, 3s1 Valence electron: 1 loses 1 electron Na Na1+ Neutral atom Sodium ion ACTIVITY 3  ACTIVITY 3 Instructions: Search for a sample of stained glass, print or cut it then paste in A4 size bond paper and discuss the chemistry concept behind it. Date of submission: NEXT WEEK Note: 1 point deduction for every day of late submission.  Lewis Structure of Ionic Compounds In ionic compound such as NaCl, a transfer of electrons from one atom to another takes place to form an ionic bond. The formation of ionic bond involves atoms with different electronegativity values. The atom with a lower electronegativity value, transfer its electron to the atom with higher electronegativity value. Metals have lower electronegativity values than nonmetals.  Example NaCl [ ][ ] 1+ 1- Na Cl Na Cl  Example Li + S → Li2S Li Li S S Li Li [ 2- Li 1+ [ S Li 1+  Lewis Structure of Ions In a Lewis structure of ions, the element symbol is placed in brackets with a superscript located at the upper right part outside the brackets, indicating the charge. As for dots surrounding the element symbol, cations will lose the number of electrons it donated, while anions will gain the number of electrons given by cations.  Example KCl [ ][ ] 1+ 1- K Cl K Cl  Example CaCl2 [ ][ ] 2+ 1- Cl Ca Cl Ca [ ] 1- Cl Cl Lewis Structure of Covalent Compounds In covalent bonding, two or more atoms share a pair (or more) of electrons to satisfy the octet rule. The formation of covalent bonds involves two or more nonmetallic elements. The electrons being shared in covalent bonding are called bonding electrons, while those valence electron pairs that are not included in the bonding are called lone pairs.  Example HCl H Cl H Cl Bonding Bonding electrons pair  Example H2O O O H H H H  Practice Problem Lewis's structure Number of electrons Element Neutral Ion Gained Lost atom 6C 35Br 13Al 37Rb