Chapter 2 The Chemical Context of Life

Chemistry Definition –Study of matter and its transformations Matter –Has mass and occupies space Transformations –Chemical reactions –Break or form chemical bonds

Units of Matter Element –Substance that cannot be broken down further by chemical means Compound –Substance composed of more than one element Molecule –Substance composed of more than one atom –Includes diatomic elements

Elements found in Living Organisms 98 % of living mass composed of 4 elements –Oxygen –Carbon –Hydrogen –Nitrogen Minerals Trace elements

The Atom Basic Unit of Elements Most fundamental unit of an element that retains the properties of the element Structure determines properties of element Composed of sub atomic particles

Subatomic Particles Proton Neutron Electron

Protons Composed of quarks –2 ups and a down – Quarkhttp://en.wikipedia.org/wiki/ Quark Positive charge of +1 Mass of 1 AMU or Dalton Resides in atomic nucleus Confers identity Atomic number

Neutrons Composed of quarks –2 downs and an up Electrically neutral Mass of 1 AMU Resides in atomic nucleus Stabilizes atomic nucleus Contributes to atomic mass Number varies Isotopes

Quarks and Leptons both Fermions

Isotopes Forms of an element that differ in the number of neutrons Atomic mass changes but atomic number does not May be radioactive if atomic nucleus is over crowded

Isotopes

Common Radioactive Isotopes

Types of Radioactive emissions Alpha –Helium nucleus –2protons, 2 neutrons Beta –Electron equivalent –Neutron converts to proton Gamma –EM radiation –Accompanies other particles G -

Electrons Fundamental particle called a lepton ton ton Electrical charge of -1 Mass negligible( 1⁄1836 of that of the proton) Located outside the atomic nucleus in the electron cloud Neutralizes the charge of the protons Participates in chemical bonding

Electron location within the Electron Cloud Distance from atomic nucleus indicates electron energy level The farther from the nucleus, the higher the energy Levels called shells (1 st quantum number,N) Named as numbers (1,2,3…) Maximum number of electrons in each shell= 2N 2 Outer shell=valence shell Outer shell electrons most readily available for chemical bonding

Electron location within the Electron Cloud Orbitals (2 nd quantum number (l) Specific region in which an electron is likely to be found Named with letters –s- sharp –p-principal –d- diffuse –f-fundamental –Named after groups of lines in the spectra of alkali metals

Electron location within the Electron Cloud Shapes of orbitals s spherical- 2 electrons p party balloons- 6 e - d complex 10 e - f complex 14 e - Energy increases from s-f Electrons usually fill from s→f with some exceptions 3 rd quantum number is the axis or magnetic orientation of the orbital (m)

Electron Fill Electron configuration of an element Fill from lowest energy to highest energy location Opposite spins for electrons in same orbital (Pauli exclusion principle) Spin is the 4 th quantum number (s)

Sub Atomic Particles ProtonNeutronElectron Mass (kg) x x x Charge [C] Radius8x less than Compositio n uuddduN/A

Periodic table Periods –Horizontal rows –Represent electron filling of a shell –Fill from left to right –s 1 st 2 groups –d transition metal –p right block, metaloids, non metals –f lanthides and actinides

Electron configurations C N O Li Cl F Ne

Bohr Model C N O Li Cl F Ne

Chemical bonding Forms by interactions between valence shell electrons Goal- full valence shell Two main types –Ionic –Covalent Type determined by electro negativity differential

Ionic Bonds Electron transfer Large electro negativity differential Between metals and non metals Ions formed –Cation –Anion Attraction between oppositely charged ions

Covalent Bonds Electrons shared between atoms Low electro negativity differential Hybrid orbitals Electron timeshare Single Double Triple

Polar Covalent Bonds Electrons not shared equally Creates a dipole Rotates in electrical field Fosters dipole interactions

Non-Polar Covalent Bonds No separation of charges Equal electron sharing Even distribution of charges Fosters induced dipole interactions

Dipole Interactions Occur between polar covalent molecules Stronger than interactions between non- polar molecules Slightly negative region of one molecule is attracted to slightly positive region of a neighboring molecule Cohesive

Hydrogen Bonds Special type of dipole interaction Involves H as the slightly + component Very significant in biological systems –2 strands of DNA –Protein shape –Genetic code

Induced Dipole Interactions May be referred to as Van der Waals interactions Very weak Between non-polar covalent molecules Volatility of non-polars compared to polars

Induced Dipole Interaction

Solubility Like dissolves like Test for polar substance- dissolve in water Non polar solvents clean non polar stains Polar solvents clean polar stains Oil and water