Chemistry Chapter 2 - Atoms
Chemistry Chapter 2 - Atoms 1023
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This 8 page Study Guide was uploaded by Caroline Wescoe on Tuesday October 18, 2016. The Study Guide belongs to 1023 at Temple University taught by Dr. Jim Bloxton in Fall 2016. Since its upload, it has received 3 views. For similar materials see Principles of Chemistry (CH 1021) in Chemistry at Temple University.
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Date Created: 10/18/16
Chemistry Chapter 2 – Atoms Classification of Matter Compound: A pure substance that is made up of two or more elements in a fixed ratio by mass Formula of a compound: tells us the ratios of its constituent elements and identifies each element by its atomic symbol - NaCl: the ratio of sodium atoms to chlorine atoms in sodium chloride is 1:1 - H2O: the ratio of hydrogen atoms to oxygen atoms in water is 2:1 Element: A substance (for example, carbon, hydrogen, and iron) that consists of identical atoms - There are 118 known elements - Of these, 98 occur in nature; the others have been made by chemists and physicists - Their symbols consist of one or two letters Mixture: A combination of two or more pure substances - The substances may be present in any mass ratio - Each substance has a different set of physical properties - Mixtures may be homogeneous or heterogeneous - If we know the physical properties of the individual components of the mixture, we can use physical means to separate the mixture into its component parts A Water Molecule Dalton’s Atomic Theory • John Dalton (1766-1844) • All matter is composed of very tiny particles, called atoms • All atoms of the same element have the same chemical properties; Atoms of different elements have different chemical properties • Compounds are formed by the chemical combination of two or more of the same or different kinds of atoms • Molecules are a tightly bound combination of two or more atoms that acts as a single unit Law of Conservation of Mass - Matter can be neither created nor destroyed - Any chemical reaction just changes the attachments among atoms and does not destroy the atoms themselves - Monatomic elements consist of single atoms o helium (He) and neon (Ne) - Diatomic elements: There are seven elements that occur as diatomic molecules o H , N , O , F , Cl , Br , and I 2 2 2 2 2 2 2 - Polyatomic elements: Some elements have three or more atoms per molecule o O ,3P ,4S 8 o Diamond has millions of carbon atoms bonded together to form one gigantic cluster Subatomic Particles • The unit of mass is given in atomic mass units (amu) Mass and Atomic Number Mass number: The sum of the number of protons and neutrons in the nucleus of an atom • The mass of the electrons in an atom is so small compared to that of its protons and neutrons that electrons are not counted in determining mass number Atomic number: The number of protons in the nucleus of an atom Isotopes Isotopes: Atoms with the same number of protons but a different number of neutrons • Carbon-12 has 6 protons and 6 neutrons • Carbon-13 has 6 protons and 7 neutrons • Carbon-14 has 6 protons and 8 neutrons Most elements found on Earth are mixtures of isotopes • Chlorine is 75.77% chlorine-35 (18 neutrons) and 24.23% chlorine-37 (20 neutrons) Atomic Weight Atomic weight: The weighted average of the masses (amu) of the naturally occurring isotopes of an element • Example: Chlorine is 75.77% chlorine-35 and 24.23% chlorine-37 Mass of Size of an Atom Dmitri Mendeleyev (1834-1907) - Arranged the known elements in order of increasing atomic weight beginning with hydrogen - He observed that when elements are arranged in this manner, certain sets of properties recur periodically - He then arranged elements with recurring sets of properties in the same column (vertical row); Li, Na, and K, for example, fall in the same column and start new periods (horizontal rows) Classification of the Elements Metals • Are solids at room temperature (except for Hg, which is a liquid), shiny, conduct electricity, and are ductile and malleable • In chemical reactions, they tend to give up electrons Nonmetals • Except for hydrogen (H), they lie on the right side of the Periodic Table • Except for graphite, do not conduct electricity • In chemical reactions, they tend to accept electrons Metalloids • They have some of the properties of metals and some of nonmetals • they are shiny like metals but, unlike metals, do not conduct electricity • Six elements are classified as metalloids: • boron, silicon, germanium, arsenic, antimony, and tellurium • B Si Ge As Sb Te Examples of Peridicity Electron Configuration Electron configuration: The arrangement of electrons in the extra-nuclear space • The energy of electrons in an atom is quantized, which means that an electron in an atom can have only certain allowed energies Ground-state electron configuration: The electron configuration of the lowest energy state of an atom Rule 1: Orbitals fill in the order of increasing energy from lowest to highest. - For elements in the first three periods; the order is 1s, 2s, 2p, 3s, 3p, 3d Rule 2: Each orbital can hold up to two electrons with spins paired Rule 3: When there is a set of orbitals of equal energy, each orbital becomes half-filled before any of them becomes completely filled Orbital Box Diagrams - A box represents an orbital. - An arrow represents an electron. - A pair of arrows with heads in opposite directions represents a pair of electrons with paired spins. Example: carbon (atomic number 6) Electronconfiguration 2 2 1 1 Expanded: 1s 2s 2p xp y 2 2 2 1s 2s 2px2p 2y z Condensed:1s 2s 2p Electron Configuration NobleGas Orbital boxdiagram (condensed) Notation 2 2 2 2 2 1s 2s 2p [He]2s 2p Noble Gas Notation - The symbol of the noble gas immediately preceding the particular atom indicates the electron configuration of all filled shells Valence shell: The outermost incomplete shell Valence electron: An electron in the valence shell Lewis dot structure: The symbol of the element represents the nucleus and filled shells Periodic Property - the Periodic Table is constructed on the basis of trends (periodicity) in chemical properties - The Periodic Table worked because elements in the same column (group) have the same configuration in their outer shells Atomic Size The size (radius) of an atom is determined by the radius of its outermost occupied orbitals Ionization Energy Ionization energy: The energy required to remove the most loosely held electron from an atom in the gaseous state - Example: When lithium loses one electron, it becomes a lithium ion; it still has three protons in its nucleus, but now only two electrons outside the nucleus, and therefore has a positive charge - In general, it increases across a row; valence electrons are in the same shell and subject to increasing attraction as the number of protons in the nucleus increases - It increases going up a column; the valence electrons are in lower principle energy levels, which are closer to the nucleus and feel the nuclear charge more strongly
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