What are we going to Cover today Chemical Evolution Atoms and molecules Atomic mass atomic number and isotopes Orbitals and electron shells Chemical bonds Covalent bonds Electronegativity Polar covalent bonds Ionic bonds Spatial representations of the molecules The mole Cont Chemical characteristics of water pH Chemical reactions Energy The importance of carbon Functional groups Road Map of Chapter 2 Building Blocks 96 of all matter found in organisms are made of atoms of Hydrogen carbon nitrogen and oxygen Diagrams of an Atom Diagrams of atoms Electron Nucleus Hydrogen Proton Neutron Carbon Electrons are extremely small particles They orbit the nucleus of the atom They have a negative electrical charge Protons are in the nucleus and have a positive electrical charge Neutrons are found in the nucleus and have no electrical charge Forces of attraction and repulsion in the atom Particles with opposite electrical charges attract each other Particles with the same electrical charge repel each other Atomic Number and Mass Number Each element contains a characteristic number of protons Atomic number the characteristic number of protons in the nucleus of an atom This number appears as a subscript in the periodic table Mass number the amount sum of protons and neutrons in the nucleus of an atom The number of neutrons present in an element can vary The Periodic Table The atomic mass unit amu The unit use to measure the mass of the particles found in the atom The mass of each proton and neutron is virtually identical It is rounded to 1 amu The mass of each electron is 0 0005 amu Orbitals and electrical energy levels Orbitals are the specific regions around the atomic nucleus where the electrons move Each orbital can hold up to two electrons Orbitals are grouped in energy levels called electrons shells Electron shells are numbered 1 2 3 and so on The number indicates the relative distance of the electron shell from the nucleus The electrons of an atom fill the inner most shells first before filling outer shells The Structure of Some Atoms 1 Each orbital can fit a maximum of two electrons 2 There is a specific number of orbitals that can fit in an electron shell 3 The maximum number of orbitals that the first shell can hold is 1 4 The maximum number of orbitals that the 2nd and 3rd shells can hold is 4 5 The outermost shell is known as the valence shell 6 The number of electrons in the outermost shells is known as the valence electrons 7 The number of unpaired electrons in the valence shell varies among elements Some atoms have their valence shell full Such atoms are chemically stable and will not engage in chemical reactions Other atoms do not have their valence shell full Chemical Bonds Covalent Bonds Non polar Polar Ionic Bonds Covalent Bonds What are they Electronegativity Non polar covalent bonds Polar covalent bonds Types of covalent bonds Chemical Bonds Hydrogen atoms each have one unpaired electron Covalent Bonds The relationship between two or more atoms in which they share one or more pairs of electrons to fill their outermost shells Electronegativity The capacity of an atom to attract bonding electrons towards itself Each atom has an electronegativity value When there is a significant difference in the electronegativity value between two atoms a polar covalent bond is formed Example O N C or H Electronegativity of representative elements Nonpolar and polar covalent bonds Single bonds Ammonia NH3 Water H2O 1 A single covalent bond is when a pair of electrons is shared There can be one or multiple single covalent bond s Methane CH4 Double bonds 2 A double covalent bond is when two pairs of electrons are shared Carbon dioxide CO2 Triple bonds Molecular nitrogen N2 3 A triple covalent bond is when three pairs of electrons are shared Ionic Bonds What are they How are they different from covalent bonds What are forces keep them together Ionic Bonds In this type of bond atoms instead of sharing electrons completely transfer or donate electrons to another atom Ionic Bonds How the ionic bond is formed 1 Sodium now has one more proton than electron 2 Thus it is positive 3 Atoms with positive charge s are known as cations 1 Chlorine now has one more electron than proton 2 Thus chlorine is negative 3 Atoms with negative charge s are known as anions Ionic Bonds Because the atoms have now opposite electrical charges the sodium cation and the chlorine anion attract each other Na Na Cl 11 P 10 e Table salt is a crystal composed of two ions Cl17p 18e The electron sharing continuum Equal sharing of electrons Nonpolar covalent bonds atoms have no charge Hydrogen Methane Transfer of electrons Polar covalent bonds atoms have partial charge Ammonia Water Ionic bonds atoms have full charge Sodium chloride The electronegativity value of the atoms involved in the chemical bond will determine how the electrons are shared in a covalent bond and whether or not an ionic bond is formed Chemical Properties of Water Properties of water Water molecules are polar Water molecules have cohesive and adhesive properties Water is more dense as a liquid than as a solid Water has a high capacity for absorbing energy I Water is a polar molecule Oxygen is more electronegative than hydrogen Thus oxygen is going to unequally share the electrons with hydrogen This will make water a polar molecule The polarity of the water molecule will cause an attraction between opposite electrical charges among different water molecules The attraction of a positively charged hydrogen of one molecule In a body of water this interaction will take place over and over again The polarity of water molecules will allow them to interact with other polar molecules Polar molecules and ions dissolve readily in water Salt in absence of water Salt dissolved in water The molecules that interact with water are called hydrophilic Non polar compounds do not interact with water molecules Non polar compounds don t dissolve in water They interact with each other They are called hydrophobic compounds Water molecules will force them to interact with each oth II Water molecules have cohesive properties Cohesion is the attraction and binding between like molecules Water has cohesive properties This property is the result of the hydrogen bonds that occur between water molecules II Water molecules have adhesive properties Adhesion is the binding between unlike different molecules Water molecules can bind adhere with any polar or charge component such as the walls