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Compounds and molecules: • Molecule is made of two or more atoms that are chemically bonded. • compound is made of two or more elements that are chemically bonded. • Chemical bonds are the forces that hold atoms or ions together in a compound. • Chemical structure is the way, the atoms or ions are arranged in a substance. • Bond length is the distance between the nuclei of two bonded atoms. • Bond angle is the angle formed by two bonds to the same atom. Chemical bonds, bond length, bond angle • Chemical bonds can • Water is a liquid at room bend, stretch, and temperature because of rotate without the attraction between breaking. water molecules. • The strength of all chemical bonds is different, that depends on type of molecule. Characteristics of chemical bonds: • The ball and stick model shows the bond angle in a molecule of H2O • Bond length is given in picometer- (pm) is equal to 1 x 10-12 • The space-filling model of water shows that each hydrogen atom takes up less space than the oxygen atom, It determines the relative size of atoms in a compound. • Structural formula shows the structure of compound in specific arrangement of bonded atoms. Structure of compounds and their properties: • The chemical structure of compound determines the properties of that compound. • Compounds with network structures are strong solids like diamonds, silicon dioxide- quartz. They have high melting point, rigid, very hard and inflexible. • Some network solids are made of bonded ions like sodium chloride (table salt). The strong attraction between the oppositely charged ions give high melting points and boiling points. Molecular compound: covalent comp. • Some compounds are made of molecules. For example, Sugar-C12H22O11 is molecule. Like, oxygen-O2, Nitrogen-N2 are molecular compounds. • Very weak force of attraction is existing between molecules, they exist as solids, liquids or gases. Melting points and boiling points depend on their physical state and type of chemical bonds involve in the molecules. • Water is liquid at room temperature because of the attractions between water molecules that is known as Hydrogen bond, and strong covalent bonds exist in H2O, between H & O Types of Chemical Bonds • Octet rule: Each atom try to acquire system of 8–electrons if possible that is considered as most stable electron configuration. • Cause of formation of chemical bonds: Generally, atoms join to form bonds so that each atom has a stable electron configuration. • There are different types of chemical bonds. – Ionic bonds – Covalent bonds – Co-ordinate covalent bonds – Metallic bonds Ionic bonds • Ionic bonds: The attractive force arising between oppositely charged ions when electrons are transferred from one atom to another. Ionic bonds in ionic compounds: • In above diagram, the sodium atom has only one electron in outermost shell, it loses one valence electron while Chlorine atom gains that electron to complete its octet-system of 8-electrons. As a result, NaCl comp. is formed. • Sodium atom becomes positive ion by losing electron and Chlorine atom becomes negative ion by gaining electron. Therefore Na+ and Cl- combine forming ionic bond between them. • Ionic compounds are in the form of network. They don’t conduct electric current in solid state, but on dissolving or melting they are good conductors of electric current. Covalent bonds: • Covalent bond: A bond is formed when atoms share one or more pairs of electrons. Two chlorine atoms (below) share electrons equally to form a nonpolar covalent bond. Covalent bonds are often shown as a single line drawn between two atoms. The model at left shows that the two chlorine atoms share two electrons (1-pair). Dots represent electrons that are not involved in bonding. Covalent bond…… • Two chlorine atoms (above diagram) share electrons equally to form a nonpolar covalent bond. • Covalent bonds are often shown as a single line drawn between two atoms. The model at left shows that the two chlorine atoms share two electrons (1-pair). Dots represent electrons that are not involved in bonding. Shared electron pairs remain exactly in the center of bonded atoms. Covalent bonds: • In formation of covalent bonds, atoms may share two or three pairs of electrons. Polar and nonpolar covalent bonds: • Nonpolar Covalent bonds: Covalent bonds are formed by sharing equal number of electrons between two similar atoms are nonpolar. EX: H-H, Cl-Cl, O=O, N≡N • Polar Covalent: Covalent bond formed between two dissimilar atoms is polar covalent bond. The shared electron pair remains more towards more electro negative atom, rather than less electro negative atom. EX: H-Cl, H-Br, N-H bonds in NH3 molecule. Comparing Ionic and Covalent compounds: Ionic Covalent compounds compounds • Structure Net work of molecules bonded ions Valence electrons Get transferred shared Electrical Good only poor conductivity when melted or dissolved State at room Solids only Solid, liquid, temperature or gas Melting & boiling Generally high Generally low points Metallic bonds: • Metallic bond: A bond formed by the attraction between positively charged metal ions and the electrons around them. – The strength of metallic bond is very high. • Metals are flexible and conduct electric current well because their atoms and electrons move freely throughout a metal’s packed structure. • All metals, like copper, iron, gold, silver nickel have metallic bonds. • All metals are solids except Mercury. • Ion: An atom caring positive or negative charge. EX: H+ , N-3 are monoatomic ions. • Polyatomic ions: An ion positive or negative made of two or more than two atoms. • Parentheses group the atoms of a polyatomic ion in chemical molecules of compounds. • EX: NH4+ • Some names of polyatomic anions relate to the oxygen content of the anion. Most of their names end with –ite or –ate. In molecule, [NH4]2CO3 → Ammonium carbonate, [NH4]+1 and [CO3]-2 join to form compound-[NH4]2CO3 Some common polyatomic ions: Some common cations (positive ions): • Ion name and symbol Ion Charge • Cesium ion, Cs+ 1+ • Lithium ion, Li+ • Potassium ion, K+ • Rubidium ion, Rb+ • Sodium ion, Na+ • Barium ion, Ba2+ 2+ • Beryllium ion, Be2+ • Calcium ion, Ca2+ • Magnesium ion, Mg2+ • Strontium ion, Sr2+ • Aluminum ion, Al3+ 3+ Some common anions (negative ions): • Element Ion Ion charge • Fluorine,F fluoride ion, F− 1− • Chlorine, Cl chloride ion, Cl− • Bromine, Br bromide ion, Br− • Iodine, I iodide ion, I− • Oxygen, O oxide ion, O2− 2− • Sulfur, S sulfide ion, S2− • Nitrogen, N nitride ion, N3− 3− Some common transition metal cations • name Ion symbol • Copper(I) ion Cu+ • Copper(II) ion Cu2+ • Iron(II) ion Fe2+ • Iron(III) ion Fe3+ • Nickel(II) ion Ni2+ • Nickel(III) ion Ni3+ • Chromium(II) ion Cr2+ • Chromium(III) ion Cr3+ • Cadmium(II) ion Cd2+ • Titanium(II) ion Ti2+ • Titanium(III) ion Ti3+ • Titanium(IV) ion Ti4+ Naming Ionic Compounds: • The names of ionic compounds consist of the names of metal ion and anion bonded with together. Ex: NaCl → Sodium chloride • Name metal ion first followed by negative ion. Use suffix “ide” with negative ion (anions). ex: Chlorine → Chloride Oxygen → Oxide • If metal ion is transition metal, then mention its oxidation number in roman numbers in small parenthesis. • Ex: Cr2O3 → Chromium(III)oxide • An ionic compounds must have a total charge zero. Ex: Cr2O3 = 2(Cr) + 3(O)=2(3+)+3(2-)=0 Naming Covalent Compounds: Prefixes used to name 1) For covalent covalent compounds: compounds of two nonmetals-elements, Prefix # of atoms numerical prefixes tell • Mono- 1 how many atoms of • Di- 2 each element are in the • Tri 3 molecule. • Tetra- 4 2) Name positive ion first • Penta- 5 followed by negative ion • Hexa 6 3) Numerical prefixes are • Hepta 7 used before name of • Octa- 8 ions and “ide” suffix is • Nona- 9 used at ending anions. • Deca- 10 Ex: N2O4 = Dinitrogen tetra oxide. Compounds Empirical formula Molar mass Molecule-formula Formaldehyde CH2O 30.03 g/mol CH2O Acetic acid CH2O 60.06 g/mol 2 × CH2O = C2H4O2 Glucose CH2O 180.18 g/mol 6 × CH2O = C6H12O6 Empirical formula: The composition of a compound in terms of the relative numbers and kinds of atoms in the simple ratio. Molecular formula: A chemical formula that shows the number and kinds of atoms in a molecule, but not the arrangement of atoms. Molar mass: The mass of one molecule in grams or sum of atomic masses of total atoms in 1-molecule in grams. Ex: H2O= 2(H)+1(O)=2(1)+1(16)=18 g/mol Calculation to find Empirical formula: • One mole of unknown compound has 36.04 g. of carbon and 6.04 g of hydrogen. What is the compound’ empirical formula? 1) Write the atomic masses Atomic masses: carbon=12 g/mol, H= 1g/mol 2) Find the molar ratio by dividing mass of element by its atomic mass. The molar ratio of elements in the compound is empirical formula of compound. Mole of carbon=36.04 g /12 g/mol = 3 mol H=6.04g/1g/mol = 6 mol Answer: E.F = C3H6 Organic compounds: • Organic compounds: An organic compound is a covalently bonded compound that contains carbon excluding carbonates and oxides. Most organic compounds also contain hydrogen, oxygen, sulfur, and phosphorus. • Our body is made of organic compounds, which play important roles in keeping the body alive. • We are using innumerable organic compounds in everyday life. Ex: alkane, alkenes, alkynes, aromatic hydrocarbons etc. Classification of Hydrocarbons: H.C.→Simplest type of organic compounds containing only carbon and hydrogen atoms are called hydrocarbons, abbreviated as H.C. Hydrocarbons-H.C. Open chain H.C. Cyclic H.C. Alkanes H.C. Aromatic H.C. Alkenes H.C. Alicyclic H.C. Alkynes H.C. Chemistry of carbon: • Carbon has 4-valences, therefore carbon atoms form four covalent bonds in organic compounds. • Arrangement of carbon atoms vary in different alkanes, alkenes, and alkynes. The structure of hydrocarbons may be a long chained, branch chained, or cyclic. Alkanes: • Alkanes: All bonds, (c-c and c-H bonds) in the structure of organic compounds are single covalent bonds. General formula is CnH2n+2 where n= # of H. • Alkane Molecular-formula Condensed structural form • Methane CH4 CH4 • Ethane C2H6 CH3CH3 • Propane C3H8 CH3CH2CH3 • Butane C4H10 CH3(CH2)2CH3 • Pentane C5H12 CH3(CH2)3CH3 • Hexane C6H14 CH3(CH2)4CH3 • Heptane C7H16 CH3(CH2)5CH3 • Octane C8H18 CH3(CH2)6CH3 • Nonane C9H20 CH3(CH2)7CH3 • Decane C10H22 CH3(CH2)8CH3 Alkenes and alkynes: • Carbon atom can join with other carbon atoms forming single, double or triple covalent bonds. This is called catenation property of carbon. • Alkenes: At least one double bond should be present between carbon atoms in the structure of H.C. compound. Ex: CH2= CH2 → Ethene • Alkynes: At least one triple bond should be present between carbon atoms in the structure of H.C. compound. Ex: CH≡CH→ Ethyne • Functional group: Atom or group of atoms present in the given organic compound that is responsible for all properties of a compound is called functional group. –OH →hydroxyl group –Cl → chloro group, -COOH → acidic group • Alcohols: Organic compounds having hydroxyl functional group are defined as alcohols. The names of alcohols end in –ol. Ex: CH3OH →methanol, C2H5 →ethanol etc. • Polymers: A large or macro molecule that is formed by more than five monomers or small units. Ex: Many ethene molecules combine to give polymer is called Polyethene. Some polymers are natural and others are artificial. Natural polymers: • Monomer: The smaller molecule that combine with other similar molecules that makes up polymer is called a monomer. • Rubber, wood, cotton, wool, starch, protein, and DNA are all natural polymers. • Polymers are widely applicable. For example, Polypropylene is molded to make plastic containers, some parts of cars and appliances. Also used to make carpet, ropes, and artificial turf for athletic fields. • A polymer’s structure determines its elasticity. Biochemical compounds • Biochemicals, which are essential to life, include carbohydrates, proteins, and DNA. • Carbohydrates are compounds which include sugar and starches and fiber; contains carbon, hydrogen, & oxygen in their structure • Carbohydrates provide energy to living things. Many carbohydrates are made of glucose and fructose. Starch is polymer chain. • Protein: An organic compound that is made of one or more chains of amino acids and that is a principal component of all cells. • Amino acid: Simple organic compounds that contain a carboxyl group and an amino group and that combine to form proteins. • DNA: It is a polymer that stores genetic information. It has a shape of a twisted ladder known as double helix. DNA is the information that the cell uses to make proteins. In DNA, cytosine, C, always pairs Guanine, G. Adenine, A, pairs with Thymine, T.
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