2.1 Elements An element is a pure substance

2.1 Elements  An element is a pure substance

2.1 Elements An element is a pure substance that cannot be broken down into simpler substances by a chemical reaction. Each element is identified by a one- or two-letter symbol. Elements are arranged in the periodic table. The position of an element in the periodic table tells us much about its chemical properties. 1 2.1 Elements 2

2.1 Elements 3 4 2.1 Elements A. Elements and the Periodic Table The elements in the periodic table are divided into three groupsmetals, nonmetals, and metalloids. Metals: They are located on the left side of the periodic table.

They are good conductors of heat and electricity. Metals are shiny solids at room temperature, except for mercury (Hg), which is a liquid. 5 2.1 Elements A. Elements and the Periodic Table Nonmetals: They are located on the right side of the periodic table. Nonmetals have a dull appearance They are usually poor conductors of heat and electricity. Nonmetals can be solids, liquids, or gases at room temperature

solid liquid gas sulfur carbon bromine nitrogen oxygen

6 2.1 Elements A. Elements and the Periodic Table Metalloids: These are located on the solid line that starts at boron (B) and angles down towards astatine (At). Metalloids have properties intermediate between metals and nonmetals Only eight elements are Metalloids: boron (B) silicon (Si) germanium (Ge) arsenic (As)

antimony (Sb) tellurium (Te) astatine (At) polonium (Po) 7 2.1 Elements B. Focus on the Human Body Building-Block Elements: The four elements that comprise 96% of the mass of the human body. oxygen (O)

carbon (C) hydrogen (H) nitrogen (N) They are found in the four main types of biological moleculesproteins, carbohydrates, lipids, and nucleic acids. 8 2.1 Elements B. Focus on the Human Body Major Minerals:

These elements are present in smaller amounts and at least 100 mg of each are needed in the daily diet. Magnesium (Mg) and sulfur (S) are found in proteins. Trace Elements: Usually less than 15 mg of each of these elements are required in the daily diet. Iodine (I) is needed for proper thyroid funtion. 9 2.1 Elements

C. Compounds Compound: a pure substance formed by chemically combining two or more elements together. A chemical formula consists of: Element symbols to show the identity of the elements forming a compound. Subscripts to show the ratio of atoms in the compound. H2O C3H8 10 How many of each type of atoms are there

in the following compounds: 1. NaCN (sodium cyanide) 2. H2S (hydrogen sulfide) 3. C2H6 (ethane) 4. SnF2 (stannous fluoride) 5. CO (carbon monoxide) 6. C3H8O3 (glycerol) 11 2.1 Elements C. Compounds Compounds can be drawn many ways:

Different elements are represented by different colors: 12 2.2 Structure of the Atom All matter is composed of the same basic building blocks called atoms. Atoms are composed of three subatomic particles: 13 2.2 Structure of the Atom Nucleus

Electron Cloud Nucleus: location of protons and neutrons dense core of the atom location of most of the atoms mass Electron cloud: location of electrons comprises most of the atoms volume mostly empty space

14 2.2 Structure of the Atom Opposite charges attract while like charges repel each other. Protons and electrons attract each other, but two electrons repel each other. 16 2.2 Structure of the Atom From the periodic table: 3

Li Atomic number (Z) is the number of protons in the nucleus. Every atom of a given element has the same number of protons in the nucleus. Different elements have different atomic numbers. A neutral atom has no net overall charge, so Z = number of protons = number of electrons 17

2.3 Isotopes A. Isotopes, Atomic Number, and Mass Number Isotopes are atoms of the same element that have a different number of neutrons. the number of protons (Z) + the number of neutrons Mass number (A) = Mass number (A) 35

Atomic number (Z) 17 # of protons = Cl 37 17 Cl

Mass number (A) Atomic number (Z) # of protons = # of electrons = # of electrons = # of neutrons =

# of neutrons = 18 For the following atoms identify: a) atomic number, b) mass number, c)number of protons, d)number of electrons, and e) number of neutrons 118 1. 50Sn 2. 195Pt a. b. c. d.

e. a. b. c. d. e. 19 2.3 Isotopes B. Atomic Weight The atomic weight is the weighted average of the masses of the naturally occurring isotopes of a particular element reported in atomic mass units.

From the periodic table: 6 C 12.01 atomic number element symbol atomic weight (amu) 20 2.3 Isotopes B. Atomic Weight

HOW TO Determine the Atomic Weight of an Element Example What is the atomic weight of chlorine? Step [1] List each isotope, its mass in atomic mass units, and its abundance in nature. Isotope Mass (amu) Isotopic Abundance 21

2.3 Isotopes B. Atomic Weight HOW TO Determine the Atomic Weight of an Element Step [2] Multiply the isotopic abundance by the mass of each isotope, and add up the products. The sum is the atomic weight of the element. 22 Calculate the atomic weight of copper, which has two isotopes with the following properties: copper-63 (62.93

amu, 69.17% natural occurrence) and copper-65 (64.93 amu and 30.83% natural occurrence). 23 2.4 The Periodic Table A. Basic Features of the Periodic Table A row in the periodic table is called a period, and a column in the periodic table is called a group. Main group elements: They consist of the tall columns on the right and left of the Periodic Table. The groups are numbered 1A8A. Transition metal elements:

These are in the 10 short columns in the middle. The groups are numbered 1B8B. Inner transition elements: They consist of the lanthanides and actinides. There are no group numbers assigned. 24 2.4 The Periodic Table A. Basic Features of the Periodic Table 25 2.4 The Periodic Table

B-1 Characteristics of Groups 1A and 2A Elements that comprise a particular group have similar chemical properties. Group Number Group Name 1A Alkali metals 2A

Alkaline earth elements Properties of Both Groups soft and shiny metals low melting points good conductors of heat and electricity react violently with water to form basic solutions 26 27

2.4 The Periodic Table B-2 Characteristics of Groups 7A and 8A Group Number 7A Group Name Halogens Properties

exist as two atoms joined together very reactive very stable 8A Noble gases rarely combine with any other elements 28

2.4 The Periodic Table C. The Unusual Nature of Carbon Carbons 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: 29 2.5 Electronic Structure An electron is confined to a specific region around the nucleus, giving it a particular energy. The regions occupied by electrons are called

principal energy levels or shells (n). The shells are numbered n = 1, 2, 3, etc. Electrons in lower numbered shells are closer to the nucleus and are lower in energy. Electrons in higher numbered shells are further from the nucleus and are higher in energy. 30 2.5 Electronic Structure Shells with larger numbers (n) are farther from the nucleus and can hold more electrons. The maximum number of electrons in each shell is given by the formula 2(n2), where n = shell number. The distribution of electrons in the first four shells:

Shell (n) Number of Electrons in a Shell 4 3 2 1 31 2.5 Electronic Structure Shells are divided into subshells, identified by the

letters s, p, d, and f. The subshells consist of orbitals. An orbital is a region of space where the probability of finding an electron is high. Each orbital can hold two electrons. Subshell Number of Orbitals Number of Electrons 32 2.5 Electronic Structure

The s orbital has a spherical shape. The p orbital has a dumbbell shape. 33 2.5 Electronic Structure 35 Electron Configurations and the Periodic Table 36

2.6 Electron Configuration Rules to Determine the Ground State Electronic Configuration of an Atom 37 2.6 Electron Configuration The electron configuration shows how the electrons are arranged in an atoms orbitals. The ground state is the lowest energy arrangement.

Rules to Determine the Ground State Electronic Configuration of an Atom Rule [1] Electrons are placed in the lowest energy orbital beginning with the 1s orbital. Orbitals are then filled in order of increasing energy. 38 Electron Configuration Rules to Determine the Ground State Electronic Configuration of an Atom Rule [2] Each orbital holds a maximum of 2 electrons. Rule [3] When orbitals are equal in energy: 1 electron is added to each orbital until all

of the orbitals are half-filled. Then, the orbitals can be completely filled. 39 2.6 Electron Configuration Orbital Diagrams An orbital diagram uses a box to represent each orbital and arrows to represent electrons. an orbital a single, unpaired

electron an electron pair Two electrons must have paired spins (opposite directions) to fit into the same orbital. 40 2.6 Electron Configuration A. First-Row Elements (Period 1) Element Orbital

Notation Electron Configuration H (Z = 1) 1 electron He (Z = 2) 2 electrons 41 2.6 Electron Configuration

B. Second-Row Elements (Period 2) Element Orbital Notation Electron Configuration Li (Z = 3) 3 electrons C (Z = 6) 6 electrons Ne (Z = 10)

10 electrons 42 Write the orbital notation and electron configuration for the following atoms 1. He 2. Be 3. B 4. N 5. F 6. Mg 43 44

Give the total number of electrons and the identity of the element with the electronic configuration: 1. 1s22s22p63s23p64s23d104p65s2 2. 1s22s22p63s23p4 3. 1s22s22p63s1 4. 1s22s22p63s23p2 46 2.6 Electron Configuration The electron configuration can be shortened by using Noble Gas Notation. Write the Symbol of the previous Noble Gas, then add

the electronic configuration of the additional electrons. Electron Configuration Noble Gas Notation element: nearest noble gas: 47 2.6 Electron Configuration

C. Other Elements Orbital Notation Element Ca 20 electrons Electron Configuration 1s 2s 2p

3s 3p 4s Noble Gas Notation 48 2.6 Electron Configuration C. Other Elements Orbital

Notation Element Cr 24 electrons 1s 2s 2p 3s 3p

4s 3d Noble Gas Notation 49 2.6 Electron Configuration C. Other Elements Element As 33 electrons

Ar = 18 electrons Orbital Notation [Ar] 4s 3d 3p Noble Gas Notation

50 2.6 Electron Configuration C. Other Elements Orbital Notation Element Eu 63 electrons [Xe] = 54 electrons [Xe]

Noble Gas Notation 51 Ge Po Au U Es 52 UuO

Bh Pm 53 [Xe]6s24f145d10 [Kr]5s24d10 [Rn]7s2 [Xe]6s25d14f5 [Rn]7s25f146d3 54 Ga Sn

Po Re Md Uub 55 2.7 Valence Electrons The chemical properties of an element depend on the number of electrons in the valence shell. The valence shell is the outermost shell (the highest value of n). The electrons in the valence shell are called valence electrons. Be

Cl 56 2.7 Valence Electrons A. Relating Valence Electrons to Group Number Elements in the same group have similar electron configurations. Elements in the same group have the same number of valence electrons. The group number, 1A8A, 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. 57 2.7 Valence Electrons A. Relating Valence Electrons to Group Number Group number: 1A 2A 3A Period 1:

H 1s1 4A 5A 6A 7A 8A He 1s2

Period 2: Li 2s1 Be B C N O F Ne 2s2 2s22p1 2s22p2 2s22p3 2s22p4 2s22p5 2s22p6

Period 3: Na Mg Al Si P S Cl Ar 3s1 3s2 3s23p1 3s23p2 3s23p3 3s23p4 3s23p5 3s23p6 2.7 Valence Electrons B. Electron-Dot Symbols 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: H C O Cl

# of Valence electrons: Electron-dot symbol: 59 Complete the table Element: N Ge B

Te Ba # of Valence electrons: Electron-dot symbol: 60 2.8 Periodic Trends A. Atomic Size Increases The size of atoms

increases down a column, as the valence e are farther from the nucleus. Decreases The size of atoms decreases across a row, as the number of protons in the nucleus increases, pulling the valence electrons in closer. 61 62

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