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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

• 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 predictableSodium + Chlorine = Sodium Chloride

Na + Cl = NaClmetal + 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 106 atoms (1,000,000)– Period of sodium (Na) atoms, all Na atoms

have the same identical physical and chemical properties

Atoms and Elements


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 Proton ElectronCharge neutral positive negativeMass 2*10-24 g 2*10-24 g 5*10-28 g

1 Dalton 1 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

Helium He Abbreviation of element

4 Atomic mass (g/mole; Daltons)

Hydrogen

• Mass = Protons + Neutrons

Atoms and Elements


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


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 ( 37Li)

(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 (1632S)

(16 electrons in 3 orbits)

Key to Electron Structure: Revised

• Previous slide plus the following• Shell is function of distance from nucleus (and

energy)– 1st shell has 1 orbit, is the lowest energy state, and has

maximum of 2 electrons (e.g., H and He)– 2nd 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


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

• 1st Shell (1 orbit; 2 electrons)– Hydrogen (1

1H; 1 electron; stable ?)

– Helium (24He; 2 electrons; stable ?)

• Periodic Table’s 1st Row– Hydrogen and Helium


• 2nd shell has 4 orbits with 2 electrons (maximum) per orbit (total of 8 electrons)

• Most stable configuration is the following:– 1st shell filled with 2 electrons– 2nd shell filled with 8 electrons

– Total of 10 electrons (1020Ne)

• 2nd row of Periodic Table– 8 elements (list and relate to the above)


• 3nd shell has 4 orbits with 2 electrons maximum per orbit (total of 8 electrons)

• Most stable configuration is the following:– 1st shell filled with 2 electrons– 2nd shell filled with 8 electrons– 3rd shell filled with 8 electrons– Total of ___ electrons (18

40Ar)

• 3nd row of Periodic Table– 8 elements (list and relate to the above)


• 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


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


Valence Electrons

• Outermost electrons in a shell (can be in multiple orbits within that shell)

• Most stable (2nd Law TD) is one in which valence shell is completely filled with electrons– Helium: 2 electrons in the 1st shell– Neon: 2 electrons in 1st shell and 8 electrons in 2nd shell (N=10)– Argon: 2 electrons in 1st shell, 8 electrons in 2nd shell, and 8 in

the 3rd shell (N= 18)– Krypton: 3 (1st), 8 (2nd), 8 (3rd) and 18 (4th shell)– Pattern with respect to the Periodic Table?

• All other elements are less stable since outermost shell is not filled

Atoms and Elements


Isotopes

• Key to behavior of an atom gleaned from the number of electrons and protons (e.g., 2

4He (# protons =___; neutrons = __)

• Hypothetical: Add 1 additional neutron (25He)

– 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 612C

– 6 protons, 6 electrons and 6 neutrons

• Carbon thirteen is 613C


• Carbon fourteen is 614C


• Oxygen sixteen is 816O

• Oxygen eighteen is 818O


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

Grade Distribution First Test

02468

10121416

47.5 52.5 57.5 62.5 67.5 72.5 78.5 82.5 87.5 92.5 97.5

Midpoint of Grade

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