CHAPTER 2 -ATOMS 3 CLASSIFICATIONS OF MATTER: 1) ELEMENT – Pure substances that cannot be broken down any further by chemical means. (composed of only 1 type of atom) i.e. copper, mercury Periodic Table – produced by Dimitri Mendeleeve (1869) elements arranged in order by atomic number Period: row in periodic table 118 known elements 88 naturally occurring elements 99% of earth and our body composed of only 10 elements (oxygen O2 most abundant) 4 most abundant elements necessary for life: H O N C Chemical Symbol – abbreviation for name of element i.e. C = carbon Ne = neon Na = sodium Element Family or Group (column): similar properties i.e. alkali metals (reactive), halogens (colored), noble gases (non-reactive) Element Classification: metals, non-metals, metalloids Metals: shiny, ductile, malleable, conductors of heat/ electricity Non-metals: dull, poor conductors of heat & electricity Metalloids (semiconductors): properties of metals & non-metals Monotomic, Diatomic, Polyatomic Elements Most are monatomic (Na, Pb, Ca) 7 are Diatomic (natural state is a diatomic molecule) H2, O2, N2, Cl2, Br2, I2, F2 Polyatomic (P4, S8) 2) COMPOUND – Pure substances made up of 2 or more elements in a fixed ratio. (composed of one type of molecule) i.e. salt, water, caffeine 3) MIXTURE – Not pure substances (composed of 2 or more different types of atoms or molecules in variable proportions) A) Homogeneous – uniform composition; i.e. air, salt water B) Heterogeneous – compositions varies in 2 or more regions i.e. oil & water Methods to Separate Mixtures: (filtration, chromatography, distillation, etc.) DIVISIONS OF MATTER MATTER (has mass and occupies space) PURE SUBSTANCE (composed of only one kind of matter) ELEMENTS (composed of only one kind of atom) COMPOUND (composed of only one kind of molecule) MIXTURE (composed of several kinds of matter) HOMOGENEOUS (same composition) HETEROGENEOUS (composition varies) ATOMS ATOM – the smallest particle of an element that shows the chemical behavior of that element. Atomic Theory - History 470 BC – Democritus, Greek Philosopher “Everything is made of small particles, he called atoms.” 1805 – John Dalton, English Chemist 1. All matter made up of tiny indivisible particles called atoms. 2. All atoms of the same element are identical to each other. 3. Atoms of different elements are different. 4. Atoms combine to form molecules. A molecule is a tightly bound group of atoms that functions as a unit. 1780 - Lavoisier, French Chemist Law of Conservation of Matter - Matter can neither be created or destroyed. CO + PbO CO2 + Pb 1780 - Proust, French Chemist “Water is water wherever you go.” 89% O and 11% H for water Law of Constant Composition - Any compound is always made up of elements in the same proportion by weight. COMPOSITION OF ATOM (Atomic Structure) 3 Basic Particles: Protons, Electrons &Neutrons Protons (p) – positive charge (+1); 1 amu; located in nucleus Electrons (e-) – negative charge (-1); 1/1835 amu; located in cloud outside nucleus Neutrons (n) – neutral; 1 amu ; located in nucleus Atoms are neutral, so # of protons = # of electrons MASS NUMBER The number of protons plus neutrons (p + n) What is the mass number of an atom with 12 protons, 12 electrons, and 13 neutrons? Ans = Electrons are not included in the mass number. ATOMIC NUMBER The number of protons (p) Determines the identity of an element What is the atomic number for helium? How many protons? How many electrons? Ans.: What element has 12 electrons, 12 protons and 13 neutrons? Ans.: IONS – Atoms or group of atoms that have lost or gained electrons Have unequal number of protons and electrons Have charges (+ or -) i.e. Potassium (K) has: 19 protons 19 electrons if lose one electron, 18 electrons, 19 protons, charge is +1 write as K+ What is the symbol for an ion with 10 electron and 12 protons? Ans.: ISOTOPES Atoms of the same element with the same # of protons, but different # of neutrons (different mass numbers) i.e C-11, C-12, C-13, C-14 Most elements have isotopes i.e. Cobalt-60 (for cancer radiation treatment) How many neutrons does Co-60 have? Ans. ATOMIC WEIGHT The weighted average of the masses of naturally occurring isotopes Example: What is the exact atomic weight? given the following: Isotope % Abundance Exact Atomic Mass C-12 C-13 98.89% 1.11% 12.00 amu 13.00 amu Calculation: C-12: 98.89/100.00 x 12.00 amu = C-13: 1.11/100.00 x 13.00 amu = _____amu + _____amu = amu ELECTRONIC STRUCTURE OF ATOMS I) SHELL (ENERGY LEVEL) A) SUBSHELL (located in shell) 1) ORBITAL (in subshell) SHELL (ENERGY LEVEL) 7 Energy (E) levels surround nucleus “like layers of an onion” max # of e- per E level: 2n2; where n = E level ORBITAL Orbitals are electron clouds Each orbital can hold up to 2 electrons Orbitals are named with # (energy level: 1-7) and letter (shape: s, p, d, f) s = sphere, p = dumbbell i.e 1s, 2s, 2p, 3s, 3p, 4s SUBSHELL All the orbitals having the same energy level and the same letter i.e. for energy level = 2 orbital 2px 2py 2pz 2s subshell shell (energy level) Electron Configuration – tells us where the electrons are located for specific elements Rules for Writing Electronic Configurations: 1. Lowest energy first (AUFBAU). (1s, 2s, 2p, 3s, 3p, 4s) 2. Only 2 electrons per orbital (Pauli Exclusion). Opposite spins Lithium: ____ electrons Orbital Box Diagram: 1s 2s Li electron config.: ____________ 3. Don’t pair them until you have to (Hund’s Rule). Nitrogen: ___ electrons Orbital Box Diagram: 1s 2s 2px 2py 2pz N electron config.: _____________ Write orbital box diagrams and electron configs. for: Element #of e- Orbital Box Diagram He Na K Noble Gas Electron Configuration: He Na K [He] e- config. Valence Electrons – electrons in the outer most shell (the one with the highest shell #) Core Electrons – electrons in the inner shells i.e. Phosphorus (P) electron configuration 1s22s22p63s23p3 Core e- valence e- Lewis Dot Structures – show valence electrons as dots and element symbol represents nucleus and core electrons i.e. .. .P. . Group # corresponds to # of valence electrons Group No. Lewis Structure 1A 2A 3A . . Be. . Li . B. 4A . . C. . 5A 6A 7A 8A . N: . .. O: .. :F: .. :Ne: . . .. . . Write the Lewis dot Structure for silicon.