MSE230 Structure and Bonding Atomic Structure and Interatomic Bonding Aisling Coughlan acoughla purdue edu 1 Key Terminology Atomic Number Z the number of protons in the nucleus Isotopes Atoms of some elements that have two or more different atomic masses Atomic Weight The weighted average of the atomic masses of the atom s naturally occurring isotopes of an element Atomic Mass Unit AMU used to compute atomic weight Mole One mole of a substance 6 022 X 1023 2 Atomic Structure atom electrons 9 11 x 10 31 kg protons 27 kg 1 67 x 10 neutrons atomic number of protons in nucleus of atom of electrons of neutral species atomic mass unit amu 1 12 mass of 12C Atomic wt wt of 6 022 x 1023 molecules or atoms 1 amu atom 1g mol C 12 011 H 1 008 all as seen on a periodic table 3 AVAGADRO S NUMBER The number of atoms needed such that the number of grams of a substance equals the atomic mass of the substance 6 022 x 1023 NA ATOMIC OR MOLECULAR WEIGHT NA x WEIGHT PER ATOM number of neutrons N number of protons Z A Z N 4 Valence electrons determine all of the following properties 1 Chemical 2 Electrical 3 Thermal 4 Optical Bohr Model 5 Wave Mechanical Model of an Atom 6 Structure of an Electron Electrons have wavelike and particulate properties This means that electrons are in orbitals defined by a probability Each orbital at discrete energy level is determined by quantum numbers Quantum n principal energy level shell l subsidiary orbitals ml magnetic ms spin Designation K L M N O 1 2 3 etc s p d f 0 1 2 3 n 1 1 3 5 7 l to l 7 Each atom is consists of the fundamental particles negatively charged electron positively charged proton and neutral neuron Shells Electrons revolve around the positively charged nucleus made of neutrons and protons in orbits called shells The shell closest to nucleus is called the K shell also called 1 shell followed by L shell or 2 shell then M shell or 3 shell Each shell can hold up to 2n2electrons where n is the shell number The K shell can hold up to 2 electrons the L shell can hold up to 8 electrons the M shell can occupy up to 18 electrons 8 Subshells Each shell is composed of one or more subshells The first K shell has one subshell called 1s the L shell has two subshells called 2s and 2p the third shell has 3s 3p and 3d A subshell is the set of states defined by azimuthal quantum number l within a shell The values l 0 1 2 3 correspond s p d and f subshells respectively The maximum number of electrons which can occupy a subshell is given by 2 2l 1 This gives two electrons in an s subshell six electrons in a p subshell ten electrons in a d subshell and fourteen electrons in an f subshell 9 N Shell n 4 M Shell n 3 L Shell n 2 K Shell n 1 Element Symbol Atomic Number Electron Configuration Hydrogen H 1 1s1 Helium He 2 1s2 Lithium Li 3 1s22s1 Beryllium Be 4 1s22s2 Boron Be 5 1s22s22p1 Carbon C 6 1s22s22p2 Nitrogen N 7 1s22s22p3 Oxygen O 8 1s22s22p4 Flourine F 9 1s22s22p5 Neon Ne 10 1s22s22p6 10 11 Electron Configuration Valence electrons those in unfilled shells Filled shells more stable Valence electrons are most available for bonding and tend to control the chemical properties example C atomic number 6 1s2 2s2 2p2 valence electrons 12 13 14 15 Ionic bonding Between and ions Requires electron transfer Between metallic nonmetallic elements 16 Example of ionic bonding 17 Covalent Bonding Requires shared electrons C has 4 valence e Ch4 needs 4 more H has 1 valence e needs 1 more Shared electrons from carbon atom Shared electrons from hydrogen atoms 18 Examples of Covalent Bonding 19 Metallic Bonding Arises from a sea of donated valence electrons Primary bond for metals and their alloys 20 Examples of Metallic Bonding 21 Secondary Bonding Arises from interaction between dipoles Fluctuating dipoles Asymmetric Electron Clouds e g Liquid H2 H2 H2 Secondary Bonding H H H H Secondary Bonding Permanent Dipoles molecule included In general secondary bonding Liquid HCl 22 Bonding Summary Type Bond Energy Comments Ionic Large Non directional ceramics Covalent Variable e g diamond Large bismuth Small Directional semiconductors ceramics polymer chains Metallic Variable e g Tungsten Large Mercury Small Non directional metals Secondary Smallest Directional inter chain polymer intermolecular 23
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