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Transcript
NIS – PHYSICAL SCIENCE Lecture 85 – Lecture 86 – Lecture 87 Types of Bonds Ozgur Unal 1 Types of Bonds What is wrong with this person? 2 Types of Bonds In a compound, atoms are held together by attractive electric forces. A chemical bond is the force that holds atoms together in a compound. A compound has different chemical and physical properties from those of the atoms that make up the compound. Remember that atoms in a compound can lose, gain or share electrons. There are two types of compounds: Ionic compounds Gain-lose electrons Covalent compounds Share electrons 3 The Ionic Bond Consider the elements K and I. What are their group numbers? How many electrons are there in their outer energy levels? K and I for the compound KI. K loses one electron K+ I gains one electron IWhat is the total charge of the compound KI? An ionic bond is the force of attraction between the opposite charges of the ions in an ionic compound. The result of this bond is a neutral compound. Metals and non-metals usually combine by forming ionic bonds. http://www.mhhe.com/physsci/chemistry/animations/chang_7e_esp/bom1s2_11.swf 4 Sharing Electrons How do Group 14 elements, such as C and Si, form compounds? Some elements share electrons to become more chemically stable. By sharing electrons, atoms can have 8 electrons in their outer energy level. 5 Sharing Electrons The attraction that forms between atoms when they share electrons is known as a covalent bond. Covalent bond forms between nonmetallic elements! A neutral particle that forms as a result of electron sharing is called a molecule. Example: CH4, H2, H2O etc. Single Covalent Bond: A single covalent bond is made up of two shared electrons. Example: A H2O molecule has 2 single covalent bonds. 6 Sharing Electrons Multiple Covalent Bonds: A covalent bond also can contain more than one pair of shared electrons multiple (double or triple) covalent bond Example: N2 triple covalent bond CO2 double covalent bond Any other examples? 7 Sharing Electrons If you were to share food with a heavy weight lifter, would you eat equal amounts of food? As pair(s) of electrons are shared in a covalent compound, the sharing might not be equal. The strength of attraction of each atom to its electrons is related to: the size of the atom the charge of the nucleus the total number of electrons the atom contains 8 Sharing Electrons Example: HCl The shared electrons feel a stronger attraction to Cl, rather than H. These shared electrons will spend more time near the Cl atom than near the H atom. As a result of this, the Cl end of the molecule will have a negative partial charge shown by δ-. The H end of the molecule will have a positive partial charge shown by δ+. Check out Figure 14!! 9 Sharing Electrons Not all molecules have unequal sharing of electrons. Example: H2, O2, N2 etc. share the electrons equally. In order to distinguish these molecules we use the terms polar and nonpolar. A polar molecule is one that has a slightly positive end and a slightly negative end Overall molecule is neutral!! Example: H2O, HF etc. A nonpolar molecule is one in which electrons are shared equally in bonds. Example: H2, CCl4 etc. 10 Properties of Compounds Recall that atoms can form two types of bonds: covalent and ionic. Example: Sugar covalent bond Salt ionic bond How do you compare the physical and chemical properties of sugar and salt? The chemical and physical properties of covalent compounds and ionic compounds are different Table 2!! Why? 11