Table 2-1 Table 2-1. Table 2-1 Table 2-1 Each element consists of unique atoms Concept 2.2: An element’s properties depend on the structure of its.

Table 2-1 Table 2-1

Each element consists of unique atoms
Concept 2.2: An element’s properties depend on the structure of its atoms Each element consists of unique atoms An atom is the smallest unit of matter that still retains the properties of an element. Atoms of the same element share similar properties. Atoms have symbols which are the same as that of the element made up of those atoms. Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Atoms are composed of subatomic particles
Relevant subatomic particles include: Neutrons (no electrical charge, mass of one atomic mass unit, or amu) Protons (positive charge, mass of 1 amu) Electrons (negative charge, mass of 1/2000 amu) ____________________________________ Dalton is a unit used to express mass at the atomic level. 1 Dalton = 1.67 x gram. Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Electrons form a cloud around the nucleus
Subatomic Particles Neutrons and protons form the atomic nucleus at the center of the atom. Electrons form a cloud around the nucleus

Cloud model Shell model Cloud of negative charge (2 electrons)
Fig. 2-5 Cloud model Shell model Cloud of negative charge (2 electrons) Electrons Nucleus Figure 2.5 Simplified models of a helium (He) atom (a) (b)

Subatomic Particles Nucleus Protons (+ charge) determine element
Electrons (– charge) form negative cloud and determine chemical behavior Neutrons (no charge) determine isotope Atom

An atom’s nucleus contains __________.
protons neutrons electrons protons and neutrons A QUESTION

An Element’s Atomic Number
Atoms of the various elements differ in number of subatomic particles An atom before interacting with other atoms is electrically neutral, i.e. in this atom: the # of protons = the # of electrons An element’s atomic number is the number of protons in its nucleus. Therefore, Atomic number = # of protons = # of electrons Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Atomic Mass number An element’s mass number is the sum of protons plus neutrons in the nucleus Mass number = # of protons + # of neutrons Atomic mass, the atom’s total mass, can be approximated by the mass number

The element lithium has 3 protons and 4 neutrons in its nucleus
The element lithium has 3 protons and 4 neutrons in its nucleus. Its mass number is __________. 1 3 7 12 A QUESTION

Bohr Model

What is the atomic # and Mass # of each of these atoms in the Bohr models

Isotopes All atoms of an element have the same number of protons but may differ in number of neutrons Isotopes are two or more atoms of an element that differ in number of neutrons. Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Electron Distribution and Chemical Properties
The distribution of electrons in the electron shells follow usually the formula: X = 2n2 Where: X is the maximum number of electrons in an electron shell and n is the number of that electron shell in terms of its distance from the nucleus.

1H 2He 3Li 4Be 5B 6C 7N 8O 9F 10Ne 11Na 12Mg 13Al 14Si 15P 16S 17Cl
Hydrogen 1H 2 Atomic number Helium 2He He Atomic mass 4.00 First shell Element symbol Electron- distribution diagram Lithium 3Li Beryllium 4Be Boron 5B Carbon 6C Nitrogen 7N Oxygen 8O Fluorine 9F Neon 10Ne Second shell Sodium 11Na Magnesium 12Mg Aluminum 13Al Silicon 14Si Phosphorus 15P Sulfur 16S Chlorine 17Cl Argon 18Ar Figure 2.9 Electron-distribution diagrams for the first 18 elements in the periodic table Third shell

The Octet Rule Valence electrons are those in the outermost shell, or valence shell The chemical behavior of an atom is mostly determined by the valence electrons Elements with a full valence shell are chemically inert The Octet Rule: Rule that a valence shell is complete when it contains eight electrons except for H and He Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Chemically Inert Elements
Stable and unreactive Inert elements have their outermost energy level fully occupied by electrons

Chemically Reactive Elements
Reactive elements do not have their outermost energy level fully occupied by electrons

Concept 2.3: The formation and function of molecules depend on chemical bonding between atoms
Atoms with incomplete valence shells can share or transfer valence electrons with certain other atoms These interactions usually result in atoms staying close together, held by attractions called chemical bonds. Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Losing, Gaining, or Sharing Electrons
Atoms having 1, 2, or 3 electrons in their valence shell tend to lose electrons. Atoms having 4 or 5 electrons in their valence shell tend to share electrons. Atoms having 6 or 7 electrons in their valence shell tend to gain or share electrons depending on their partner atom.

the number of protons in the nucleus the total number of electrons
The most important determinant of an atom’s bonding behavior is __________. the number of protons in the nucleus the total number of electrons the number of valence shell electrons the number of neutrons in the nucleus A QUESTION

Types of Chemical Bonds
1- Covalent bonds (the strongest). 2- Ionic Bonds (strong, but fragile) Hydrogen Bonds (weak). 4- Van der Waals Interactions (weak). 5- Hydrophobic Interactions (weak).

Covalent Bonds A covalent bond is the sharing of a pair of valence electrons by two atoms In a covalent bond, the shared electrons count as part of each atom’s valence shell A molecule consists of two or more atoms held together by covalent bonds Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Covalent Bonds The atoms of four elements of the human body form covalent bonds most commonly: oxygen (O) carbon (C) hydrogen (H) nitrogen (N)

Covalent Bonds Covalent bonds can form between atoms of the same element or atoms of different elements Every atom has a characteristic total number of covalent bonds that it can form, this number is called an atom’s valence. The valence of H=1, O=2, N=3, and C=4 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

An Atom’s Valence Hydrogen (valence = 1) Oxygen (valence = 2) Nitrogen
Carbon (valence = 4) H O N C

Electrons Are Shared in Covalent Bonds
Figure 2.2 Electrons Are Shared in Covalent Bonds Two hydrogen atoms can combine to form a hydrogen molecule. A covalent bond forms when the electron shells of the two atoms overlap in an energetically stable manner.

Single, double, and triple covalent bonds
Single covalent bond One pair of electrons shared e.g., between two hydrogen atoms Double covalent bond Two pairs of electrons shared e.g., between two oxygen atoms Triple covalent bond Three pairs of electrons shared e.g., between two nitrogen atoms

Nonpolar and polar covalent bonds
Atoms in a covalent bond may share electrons equally or unequally How they share is determined by electronegativity Electronegativity: Is the relative attraction of particular atom for the electrons of a covalent bond. High electronegativity = electrons spend more time orbiting the nucleus Is determined by the number of protons in the nucleus and the proximity of valence electrons to the nucleus

1H 2He 3Li 4Be 5B 6C 7N 8O 9F 10Ne 11Na 12Mg 13Al 14Si 15P 16S 17Cl
Fig. 2-9 Hydrogen 1H 2 Atomic number Helium 2He He Atomic mass 4.00 First shell Element symbol Electron- distribution diagram Lithium 3Li Beryllium 4Be Boron 5B Carbon 6C Nitrogen 7N Oxygen 8O Fluorine 9F Neon 10Ne Second shell Sodium 11Na Magnesium 12Mg Aluminum 13Al Silicon 14Si Phosphorus 15P Sulfur 16S Chlorine 17Cl Argon 18Ar Third shell

Increasing electronegativity
Copyright © The McGraw–Hill Companies, Inc. Permission required for reproduction or display. IA IIA IIIA IVA VA VIA VIIA VIIIA Increasing electronegativity 1 H 2 He 1.008 6 7 8 4.003 3 4 Atomic number 5 9 10 Li Be 1 C O B N F Ne H 6.941 9.012 Element symbol 12.01 14.01 15.99 19.00 10.81 20.18 11 12 1.008 Atomic mass number 15 16 17 Na Mg 13 14 P S Cl 18 Al Si Ar 22.99 24.31 30.97 2.07 35.45 19 20 26 26.98 28.09 39.95 K Ca 21 22 23 24 25 Fe 27 28 29 30 31 32 33 34 35 36 Sc Ti V Cr Mn Co Ni Cu Zn Ga Ge As Se Br Kr 39.10 40.08 55.85 44.96 47.87 50.94 52.00 54.94 58.93 58.69 63.55 65.38 69.72 72.64 74.92 78.96 79.90 83.80 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe 85.47 87.62 88.91 91.22 92.91 95.94 98.00 101.1 102.9 106.4 107.9 112.4 114.8 118.7 121.8 127.6 126.9 131.3 Increasing electronegaativity 55 56 57 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn 132.9 137.3 138.9 178.5 180.9 183.8 186.2 190.2 192.2 195.1 197.0 200.6 204.4 207.2 209.0 209.0 210.0 222.0 87 88 89 104 105 106 107 108 109 110 111 112 112 114 115 116 117 118 Fr Ra Ac Rf Db Sg Bh Hs Mt Ds Rg Uub Uut Uuq Uup Uuh Uus Uuo 223.0 226.0 227.0 267.0 268.0 271.0 272.0 270.0 276.0 281.0 274 277 277 289.0 288.0 293.0 292.0 294.0 58 59 60 61 62 63 64 65 66 67 68 69 70 71 Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 140.1 140.9 144.2 145.0 150.4 152.0 157.3 158.9 162.5 164.9 167.3 168.9 173.0 175.0 90 91 92 93 94 95 96 97 98 99 100 101 102 103 Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr 232.0 231.0 238.0 237.0 244.0 243.0 247.0 247.0 251.0 252.0 257.0 258.0 259.0 262.0

Nonpolar and polar covalent bonds (continued)
Atoms in a covalent bond may share electrons equally or unequally Two atoms of the same element have the same electronegativities and share electrons equally, This results in forming a nonpolar covalent bond Atoms with different electronegativity share electrons unequally This results in a polar covalent bond. Exception is the bond between carbon and hydrogen, considered nonpolar

Nonpolar Covalent Bond
In a nonpolar covalent bond, the atoms share the electron equally

Polar Covalent Bond In a polar covalent bond, one atom is more electronegative, and the atoms do not share the electron equally

Less electronegative atom develops a partial positive charge
Polar Covalent Bond More electronegative atom develops a partial negative charge Less electronegative atom develops a partial positive charge In a bond between oxygen (more electronegative) and hydrogen (less electronegative), oxygen is slightly negative, hydrogen slightly positive  –  – O H H + + H2O

Covalent Bonds What type of bond is formed between two oxygen atoms?

Why are some covalent bonds nonpolar and others polar?
Different atoms have different electronegativities and share electrons unequally, causing polar bonds. Bonds between atoms of the same type are nonpolar. (An exception is the carbon-hydrogen bond, which is considered nonpolar, though the atoms are of different types.)

Covalent bonds occur when __________.
electrons are shared between atoms electrons are transferred between atoms electrons are lost opposite charges attract atoms together A QUESTION

Atoms sometimes strip electrons from their bonding partners
Ionic Bonds Atoms sometimes strip electrons from their bonding partners An example is the transfer of an electron from sodium to chlorine After the transfer of an electron, both atoms have charges A charged atom (or molecule) is called an ion Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Ionic Bonds A cation is a positively charged ion
An anion is a negatively charged ion An ionic bond is an attraction between an anion and a cation

When atoms gain electrons __________.
the atoms become electrically neutral the atoms become positively charged their atomic mass significantly increases the atoms become negatively charged A QUESTION

Ionic Bonds Na Cl Na Cl Na Cl Na+ Cl– Sodium atom Chlorine atom
Fig Ionic Bonds Na Cl Na Cl Na Cl Na+ Cl– Sodium atom Chlorine atom Sodium ion (a cation) Chloride ion (an anion) Figure 2.14 Electron transfer and ionic bonding Sodium chloride (NaCl)

Figure 2.6 Ionic Attraction between Sodium and Chlorine
Figure 2.6 Ionic Attraction between Sodium and Chlorine When a sodium atom reacts with a chlorine atom, the chlorine fills its outermost shell by “stealing” an electron from the sodium. In so doing, the chlorine atom becomes a negatively charged chloride ion (Cl–). With one less electron, the sodium atom becomes a positively charged sodium ion (Na+).

Ionic bonds connect atoms together by __________.
overlap of valence shells charge attractions overlap of the nucleus Ionic bonds do not connect atoms together. A QUESTION

Ionic Compounds Compounds formed by ionic bonds are called ionic compounds, or salts Salts, such as sodium chloride (table salt), are often found in nature as crystals Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Comparison of Ionic, Polar Covalent, and Nonpolar Covalent Bonds
Figure 2.9

Hydrogen Bonds A hydrogen bond forms between polar molecules
attraction between a partially positive hydrogen atom and a partially negative atom individually weak, collectively strong Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Hydrogen Bond in Water

Figure 2.4 Hydrogen Bonds Can Form between or within Molecules
Figure 2.4 Hydrogen Bonds Can Form between or within Molecules (A) A hydrogen bond forms between two molecules because of the attraction between an atom with a partial negative charge on one molecule and a hydrogen with a partial positive charge on a second molecule. (B) Hydrogen bonds can form between different parts of the same large molecule.

Hydrogen atom Hydrogen bond C H + O O C O C  O Oxygen atom C H C +
Copyright © The McGraw–Hill Companies, Inc. Permission required for reproduction or display. Hydrogen atom Hydrogen bond C H + O C O O C  O Oxygen atom C C H + C O O Water molecule O Glucose molecule

  + Water (H2O) + Hydrogen bond   Ammonia (NH3) + + +
Fig. 2-16   + Water (H2O) + Hydrogen bond   Ammonia (NH3) Figure 2.16 A hydrogen bond + + +

Hydrogen bonds are similar to ionic bonds because __________.
both hydrogen bonds and ionic bonds are due to opposite charge attractions they both occur between like charged atoms they both form molecules they are both very strong bonds A QUESTION

Table 2-1 Table 2-1. Table 2-1 Table 2-1 Each element consists of unique atoms Concept 2.2: An element’s properties depend on the structure of its.

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Table 2-1 Table 2-1. Table 2-1 Table 2-1 Each element consists of unique atoms Concept 2.2: An element’s properties depend on the structure of its.

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