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Atoms and the Periodic Table.  A pure substance that cannot be broken down into simpler substances by a chemical reaction  Identified by a one- or.

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Presentation on theme: "Atoms and the Periodic Table.  A pure substance that cannot be broken down into simpler substances by a chemical reaction  Identified by a one- or."— Presentation transcript:

1 Atoms and the Periodic Table

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3  A pure substance that cannot be broken down into simpler substances by a chemical reaction  Identified by a one- or two-letter symbol  Arranged in the periodic table  Its location on the periodic table indicates a lot about its chemical properties  Can be a metal, nonmetal, or a metalloid

4  Some of the element symbols will be familiar to you already  It will take time and practice to learn others

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7  Metals- located to the left of the stair step line (top located near Boron) ◦ Shiny ◦ Good conductors of heat and electricity ◦ Solid at room temperature except for mercury

8  Nonmetals – except for hydrogen (H) these are located to the right of the stair step line (top located near Boron) ◦ Do not have a shiny appearance ◦ Generally poor conductors of heat and electricity ◦ Usually a solid or gas at room temperature (exception: Br 2 is a liquid at room temperature)

9  Metalloids – 7 elements located along the stair step line (top located near Boron) ◦ Properties in between metals and nonmetals ◦ Metallic shine but brittle  Boron (B)  Silicon (Si)  Germanium (Ge)  Arsenic (As)  Antimony (Sb)  Tellurium (Te)  astatine (At)

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11  A pure substance formed by chemically combining two or more elements  A chemical formula for a compound consists of: ◦ Element symbols to show the identity of the elements that form a compound ◦ Subscripts to show the ratio of atoms in the compound H2OH2O 2 H atoms1 O atom C3H8C3H8 3 C atoms8 H atoms H2OH2OC3H8C3H8

12  Can be drawn many ways but we are always making a simplified representation of reality

13 O H Line Lewis Dot Diagram

14  All mater is composed of building blocks called atoms  Atoms are composed of three subatomic particles ◦ Proton ◦ Neutron ◦ Electron

15  The mass of an atom is very small since each proton and neutron has a mass of X  Chemists use the atomic mass unit (amu) to measure the mass of an element

16  The nucleus is the dense core that contains the protons and neutrons  Most of the mass of an atom is in the nucleus  Electron cloud is composed of electrons that are in almost empty space around nucleus

17  Opposite charges attract each other  Like charges repel each other  Protons and electrons attract each other but electrons repel each other

18  The number of protons in the nucleus of an atom is its atomic number ◦ Every atom of a given element has the same number of protons in the nucleus  We can symbolize the number of protons with the generic letter Z  A neutral atom has no overall chare so: ◦ Z= number of protons = electrons  Example: Lithium 3 Li Atomic number (Z) is the number of protons in the nucleus.

19  Atoms of the same element that have a different number of neutrons ◦ The number of protons remains constant  Different forms of the same element  The mass number (A) represents the number of protons plus the number of neutrons ◦ A = Z + number of neutrons  Example – two forms of carbon: ◦ C-12 has 6 neutrons ◦ C-14 has 8 neutrons ◦ Z = 6 for both forms of carbon

20 35 17 Cl Mass number (A) Atomic number (Z) # of protons = 17 # of electrons = 17 # of neutrons = A – Z = 35 – 17 = 18

21  The weighted average of the masses of the naturally occurring isotopes of a particular element reported in atomic mass units (amu) ◦ This information can be found on the periodic table 6 C atomic number (Z) element symbol atomic weight (amu)

22  The weighted average of the ass of the naturally occurring isotopes Example Step [1] What is the atomic weight of chlorine? List each isotope, it’s mass in atomic mass units, and it’s abundance in nature. Mass (amu) Isotopic AbundanceIsotope Cl-35 Cl % = % =

23 Step [2] Multiply the isotopic abundance by the mass of each isotope, and add up the products x x = = amu amu amu = amu Answer 4 sig. figs. The sum is the atomic weight of the element. 4 sig. figs.

24  Periodic table was put together over time as the elements were discovered, isolated, and studied.  Many versions exist but the most common is based on the one developed by Dmitri Mendeleev in 1869  A row in the periodic table is called a period ◦ Elements in the same row are similar in size  A column in the periodic table is called a group ◦ Elements in the same group have similar electronic and chemical properties

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26 1A2ABB7A8A Alkali MetalsAlkaline Earth Metals Transition Metals Lanthanide & Actinide HalogensNobel Gases Very reactive Metals except for H +1 ions React with Oxygen to form compounds that dissolve into alkaline solutions in water Reactive +2 ions Oxygen compounds are strongly alkaline Many are not water soluble Metals Form ions with several different charges (oxidation states) Tend to form +2 and +3 ions Lanthanides 58 – 71 Actinides 90 – 103 Actinides are radioactive Reactive Form diatomic molecules in elemental state -1 ions Salts with alkali metals Inert Heavier elements have limited reactivity Do not form ions Monoatomi c gases

27  Carbon’s ability to join with itself and other elements gives it a versatility not seen with any other element in the periodic table  Elemental forms of carbon include the following carbon-only structures: diamondgraphitebuckminsterfullerene

28  “the party animal of the atomic world, latching onto many other atoms (including itself) and holding tight, forming molecular conga lines of hearty robustness-the very trick of nature necessary to build proteins and DNA” ◦ Bill Bryson from A Short History of Nearly Everything

29  The chemical properties of an element are determined by the number of electrons in an atom ◦ Electrons do not move freely in space – restricted to a region with a particular energy ◦ Electrons occupy discrete energy levels that are restricted to specific values – the energy is “quantized”  Electrons are confined to regions called the principal energy levels or shells

30  The shells are numbers, n=1, 2, 3, 4… Moving out from the nucleus  Electrons closer to the nucleus are held more tightly are lower in energy  Electrons farther from the nucleus are held less tightly and are higher in energy  The farther a shell is from the nucleus, the larger its volume, and the more electrons it can hold

31 Nucleus

32  Each shell is divided into subshells made up of orbitals ◦ These are identified as s, p, d, f  Each orbital can hold two electrons

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34  The maximum number of electrons that can occupy a shell is determined by the number of orbitals in a shell

35  The electron configuration shows how the electrons are arranged in an atom’s orbitals  The ground state is the lowest energy arrangement  The outtermost shell is the valance shell  The electrons in the valence shell are called valence electrons  The chemical properties of an element depend on the number of electrons in the valence shell

36  Rule 1: ◦ Electrons are placed in the lowest energy orbital beginning with the 1s orbital. ◦ Orbitals are then filled in order of increasing energy.  Rule 2: ◦ Each orbital holds a maximum of 2 electrons  Rule 3: ◦ 1 electron is added to each orbital until all of orbitals are half-filled ◦ Then, the orbitals can be completely filled

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38  What would the electron configuration for fluorine (F) be? ◦ Atomic Number = 9 so it has nine electrons ◦ Shells fill: 1s 2 2s 2 2p 5  How many valence electrons does it have? ◦ There are 7 electrons in the 2 nd shell so there are 7 valence electrons

39 Be 1s22s21s22s2 Cl 1s22s22p63s23p51s22s22p63s23p5 valence shell: n = 2 # of valence electrons = 2 valence shell: n = 3 # of valence electrons = 7 Atomic number: 4Atomic number: 17

40  Elements in the same group have similar electron configurations.  Elements in the same group have the same number of valence electrons.  The group number, 1A–8A, equals the number of valence electrons for the main group elements.  The exception is He, which has only 2 valence electrons.  The chemical properties of a group are therefore very similar.

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42  Dots representing valence electrons are placed on the four sides of an element symbol  Each dot represents one valence electron  For 1 to 4 valence electrons, single dots are used  With more than 4 valence electrons the dots are paired Element: # of Valence electrons: Electron-dot symbol: H 1 C 4 O 6 Cl 7 HCO

43 The size of atoms increases down a column, as the valence e − are farther from the nucleus. The size of atoms decreases across a row, as the number of protons in the nucleus increases, pulling the valence electrons in closer. Increases Decreases

44 The ionization energy is the energy needed to remove an electron from a neutral atom. Na + energyNa + + e – Ionization energies decrease down a column as the valence e − get farther away from the positively charged nucleus. Increases Ionization energies increase across a row as the number of protons in the nucleus increases.


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