Atoms and Elements Matter and Elements Atoms Particles Atomic Structure Electrons Periodic Table Electrons in Shells Valence Electrons Isotopes

Take Home Message Atoms are the chemical building blocks of all matter Structure of atoms (electrons, neutrons, protons and their arrangement) determine the unique behavior/attributes of the elements Of the above (No. 2), the “place” and “pairing” of the electrons are the most critical Electrons reside in defined shells (orbits) surrounding the nucleus of the atom and the electrons in the outermost shell (valence electrons) determine an atom’s chemical reactivity Utility and periodicity of the Periodic Table of Elements is a function of the valence electrons in the outermost shell and the mass of the element

Atoms and Elements Matter and Elements Atoms Particles Atomic Structure Electrons Periodic Table Electrons in Shells Valence Electrons Isotopes

Matter and Elements Phases of Matter –Shape and volume Gas (no definite shape nor definite volume) Liquid (definite volume but no definite shape) Solid (definite shape and definite volume)

Elements Substances that can not be broken down by chemical reaction Hierarchy Compound Element Atom Subatomic Particle

Elements Patterns –92 naturally occurring elements (e.g., hydrogen, gold, helium, sulfur, carbon, uranium) –26 short-lived or artificially yielded elements –Total of 118 –25 of 92 are essential to life (e.g., ?????) –Earth’s mass is predominantly six elements (oxygen, sulfur, magnesium, iron, aluminum and calcium) Key points –any element is the same in its chemical structure and physical properties (~stable over time) –All elements have their origin in either the big bang (hydrogen and helium) or the subsequent evolution of the universe

Elements Compound –Elements combine in very precise ways that are recurrent and predictable Sodium + Chlorine = Sodium Chloride Na+Cl = NaCl metal + gas = solid Key points: –atom of sodium (Na) remains an atom of sodium (as for chlorine) –Emergent property: “creation” of new properties in a compound that can not be explained by the summation of the two elements (hierarchy theory)

Atoms and Elements Matter and Elements Atoms Particles Atomic Structure Electrons Periodic Table Electrons in Shells Valence Electrons

Atoms Definition: smallest unit of an element that retains properties of an element (e.g., gold, sodium) Observations –Period has 10 6 atoms (1,000,000) –Period of sodium (Na) atoms, all Na atoms have the same identical physical and chemical properties

Atoms and Elements Matter and Elements Atoms Particles Atomic Structure Electrons Periodic Table Electrons in Shells Valence Electrons

Particles Atoms are composed of particles (subatomic particles) Most stable particles –Neutrons –Protons –Electrons Other less stable particles (quarks, neutrinos, etc.) Relationship among the more stable particles Neutron ProtonElectron Chargeneutralpositivenegative Mass 2* g 2* g 5* g 1 Dalton1 Dalton

Atomic Structure Atoms of the same elements (e.g., hydrogen, helium, gold) have the same number of subatomic particles and by convention we abbreviate as follows: 2# of protons HeliumHeAbbreviation of element 4Atomic mass (g/mole; Daltons) Hydrogen Mass = Protons + Neutrons

Atoms and Elements Matter and Elements Atoms Particles Atomic Structure Electrons Periodic Table Electrons in Shells Valence Electrons

Atomic Structure Example of sodium (Na) 11 Na 23 Mass = Protons + Neutrons 23 = 11 + ? Protons = Neutrons = Electrons = If atom is neutral (not charged), # protons always equals # electrons If atom is charged (“ionized”), # protons does not equal the # electrons and atom is charged (ion) –Positive ion (# protons > # electrons) –Negative ion (# electrons > # protons)

Atoms and Elements Matter and Elements Atoms Particles Atomic Structure Electrons Periodic Table Electrons in Shells Valence Electrons

Electrons Energy “barons” of the atom (motion) –Energy = ability to do work –Potential energy = energy stored due to position or location Charge is negative (-) and particle is always in motion Capturing an atom and its orbiting electron

Electrons Re-capture the same atom Distance of electron from nucleus is always the same but the location varies (distance is synonymous with energy) Keys –Nucleus is stationary –Electron moves constantly with energy (chemical) –Distance is the same Relate to last week’s lecture (Bohr’s atom and quantum levels)

Electrons Re-capture the same atom Re-capture to create a “fuzzy orbit” around the nucleus (1 orbit and 1 electron) Example of Lithium ( 3 7 Li) (3 electrons in 2 orbits)

Key to Electron Structure Count the number of electrons (and compare with abbreviation of element) Electrons are negative in charge and in constant motion Electrons are in orbits around the nucleus Chemists sometimes refer to orbits as “shells” See word slide + 2

Electrons Example of Sulfur ( S) (16 electrons in 3 orbits)

Key to Electron Structure: Revised Previous slide plus the following Shell is function of distance from nucleus (and energy) –1 st shell has 1 orbit, is the lowest energy state, and has maximum of 2 electrons (e.g., H and He) –2 nd shell has 4 orbits and a maximum of 8 electrons (2 electrons per orbit) If electron possess energy, it can loose or gain that energy –Loose energy…drops down to a lower shell –Gains energy…jumps to a higher shell (remember Bohr and quantum numbers)

Example of Electrons in Shells As electrons move between shells, they change potential energy –Hot summer day, bright sun and car top Light absorption by pigments and electrons “jump” to higher shell (potential energy); give off energy when they drop back (kinetic energy) –Banana, orange juice or bagel this AM? Excited electron is “capture” by chlorophyll in leaf and shuffled to a sugar molecule in its excited state (potential energy) until you release the energy via digestion/respiration by allowing the electron to “drop back” to a lower level (kinetic energy)

Key to Electron Structure: Revised Again Electrons reside in shells as a function of quantum mechanics (1-4 orbits per shell) Never more than 2 electrons per orbit (Pauli Exclusion Principle) Distribution of electrons is key to understanding why elements behave the way they do and why the Periodic Table “works” Outermost electrons are called the valence electrons: special significance

Atoms and Elements Matter and Elements Atoms Particles Atomic Structure Electrons Periodic Table Electrons in Shells Valence Electrons

Periodic Table of Elements Concept: most stable state for an atom is one in which the outer shell is filled with the maximum number of electrons 1 st Shell (1 orbit; 2 electrons) –Hydrogen ( 1 1 H; 1 electron; stable ?) –Helium ( 2 4 He; 2 electrons; stable ?) Periodic Table’s 1 st Row –Hydrogen and Helium

Periodic Table of Elements 2 nd shell has 4 orbits with 2 electrons (maximum) per orbit (total of 8 electrons) Most stable configuration is the following: –1 st shell filled with 2 electrons –2 nd shell filled with 8 electrons –Total of 10 electrons ( Ne) 2 nd row of Periodic Table –8 elements (list and relate to the above)

Periodic Table of Elements 3 nd shell has 4 orbits with 2 electrons maximum per orbit (total of 8 electrons) Most stable configuration is the following: –1 st shell filled with 2 electrons –2 nd shell filled with 8 electrons –3 rd shell filled with 8 electrons –Total of ___ electrons ( Ar) 3 nd row of Periodic Table –8 elements (list and relate to the above)

Periodic Table of Elements Rows –Number of elements in a row is not chance but reflects the maximum number of electrons in a shell Row 1 = 2 Row 2 = 8 Row 3 = 8 Row 4 = 18 etc

Periodic Table of Elements Columns –Elements in a given column have similar chemical properties –All elements in column have the same number of valence electrons –Column IA has 1 electron in outer shell –Column IIA has 2 electrons in outer shell –Column IIIB has 3 electrons in outer shell –Column VA has 5 electrons in outer shell

Atoms and Elements Matter and Elements Atoms Particles Atomic Structure Electrons Periodic Table Electrons in Shells Valence Electrons

Outermost electrons in a shell (can be in multiple orbits within that shell) Most stable (2 nd Law TD) is one in which valence shell is completely filled with electrons –Helium: 2 electrons in the 1 st shell –Neon: 2 electrons in 1 st shell and 8 electrons in 2 nd shell (N=10) –Argon: 2 electrons in 1 st shell, 8 electrons in 2 nd shell, and 8 in the 3 rd shell (N= 18) –Krypton: 3 (1 st ), 8 (2 nd ), 8 (3 rd ) and 18 (4 th shell) –Pattern with respect to the Periodic Table? All other elements are less stable since outermost shell is not filled

Atoms and Elements Matter and Elements Atoms Particles Atomic Structure Electrons Periodic Table Electrons in Shells Valence Electrons Isotopes

Key to behavior of an atom gleaned from the number of electrons and protons (e.g., 2 4 He (# protons =___; neutrons = __) Hypothetical: Add 1 additional neutron ( 2 5 He) –Electrons = ____ –Protons = ____ –Chemical behavior of atom changed or unchanged? Isotope: each element has –Fixed number of protons (Periodic Table) –Fixed number of electrons (Periodic Table) –Number of neutrons may vary –Atoms of same element with same number of protons but different number of neutrons are called stable isotopes –Not radioactive isotopes

Isotopes Carbon twelve is 6 12 C –6 protons, 6 electrons and 6 neutrons Carbon thirteen is 6 13 C –6 protons, 6 electrons and 7 neutrons Carbon fourteen is 6 14 C –6 protons, 6 electrons and 8 neutrons Oxygen sixteen is 8 16 O Oxygen eighteen is 8 18 O –8 protons, 8 electrons and 10 neutrons

Take Home Message Atoms are the chemical building blocks of all matter Structure of atoms (electrons, neutrons, protons and their arrangement) determine the unique behavior/attributes of the elements Of the above (No. 2), the “place” and “pairing” of the electrons are the most critical Electrons reside in defined shells (orbits) surrounding the nucleus of the atom and the electrons in the outermost shell (valence electrons) determine an atom’s chemical reactivity Utility and periodicity of the Periodic Table of Elements is a function of the distribution of all electrons in shells, the valence electrons in the outermost shell, and the mass of the element