Unit 3 Flashcards
Atomic theory
- All matter is composed of atoms.
- The atoms of a given element differ from the atoms of all other elements.
- Chemical compounds consist of atoms combined in specific ratios. Only whole atoms can combine.
- Chemical reactions change only the way atoms are combined in compounds.
Subatomic particles
Protons + charge
Neutrons electrically neutral (similar mass to proton)
Electrons - charge
Mass is only 1/1836 of proton
Atomic mass unit (amu)
Unit for describing the mass of an atom, based on the mass of a carbon-12 atom
Proton +1 charge
Neutron 0 charge
Electron -1 charge
Subatomic particles arranged:
Protons and neutrons packed tightly in nucleus
Electrons surround the nucleus and move rapidly through large volume of space
Atomic number
Mass number
Atomic number = #protons
Mass number = p+n
In a neutral atom p = e
Therefore,
N = mass# - atomic#
In textbook mass # A
Atomic # Z
Isotopes
Atoms of the same element
Have different mass numbers
Same # of protons but
Different # of neutrons
Can be distinguished by their atomic symbols
Ex. Isotope favor uranium identified as U-235 to uranium-235
Metal
A malleable element, with a lustrous appearance, that is a good conductor of heat and electricity
– Metals occur on the left side of the periodic table.
Nonmetal
An element that is a poor conductor of heat and electricity
– Nonmetals occur on the upper- right side of the periodic table.
Metalloid
An element whose properties are intermediate between those of a metal and a nonmetal
– Metalloids are located in a zigzag band between the metals on the left and nonmetals on the upper- right side of the periodic table.
Elements in the same vertical column (group)
Have similar physical and chemical properties
Group 1A—Alkali metals
• Shiny, soft metals with low melting points
• React with water to form products that are highly alkaline
• Highly reactive
• never found in nature in a pure state.
Group 2A—Alkaline earth metals
• Lustrous, silvery metals
• Less reactive than their neighbors in group 1A
• Never found in nature in a pure state
Group 7A—Halogens
• Colorful and corrosive nonmetals
• Found in nature only in combination with other elements, such as with sodium in table salt (sodium chloride, NaCl)
Group 8A—Noble Gases
• Colorless gases
• Labeled the “noble” gases because of their lack of chemical reactivity
Valence electrons and group number
Elements in the same group have similar chemical properties because they have the same number of valence electrons and can undergo the same types of chemical reactions
Periodicity
Repeating rise and fall pattern
Metallic character
Trend
atoms that lose electrons easily to form ions have more metallic character and relates to the ionization energy of elements.
Increases from top to bottom and right to left
Atomic radius trend
Increases from top to bottom and right to left
Ionization energy trend
Increases from bottom to top and from left to right on periodic table
• energy absorbed to remove one electron from a single atom in the gaseous state.
Electron affinity trend
Increases from bottom to top and from left to right on periodic table
Energy released on adding an electron to a single atom in the gaseous state
Quantum mechanical model developed by Erwin Schrodinger
Helps us understand the electronic structure of atoms:
• Electrons have both particle-like and wavelike properties.
• The behavior of electrons can be described using an equation
called a wave function.
• Electrons are not perfectly free to move. They are restricted to
certain energy values, or quantized.
Periodic trends
Electrons and energy levels
• Electrons with the same energy are grouped in the same
energy level.
• Electrons farther away from the nucleus— increase in
energy as the value of n increases
• Shells farther from the nucleus can hold more electrons
Wave functions also provide an electron with an “address” within an atom, composed of shell, subshell, and orbital.
Shell/Principal Energy Level (n): A grouping of electrons in an atom according to energy
Shell number (n): 1 2 3 4
Electron capacity: 2 8 18 32
Sublevels
-The arrangement of electrons determines the physical and chemical properties of an element.
• Each energy level/shell (n) consists of one or more sublevels.
• The number of sublevels in an energy level is equal to the principal quantum
number (n) of that energy level.
•So, if n =1,then 1 sublevel
• n=2, then 2 sublevels, etc.
• The sublevels are identified as s, p, d, and f.
• The order of sublevels in an energy level is
s<p<d<f
(electrons in s sublevel have least E, those in f have most E)
Pauli exclusion principle states that
-each orbital can hold a maximum of two electrons.
-electrons in the same orbital repel each other.
-electrons in the same orbital must have their magnetic spins cancel (they must spin in opposite directions).
-We can represent magnetic spins with arrows
Electronic structure of atoms
• s subshell has 1 orbital
• p subshell has 3 orbitals
• d subshell has 5 orbitals
• f subshell has 7 orbitals.
Each orbital holds two (2) electrons, which differ in a property known as spin.
Orbital diagrams
• are arranged in the orbitals of an atom.
• fill the orbitals and energy levels from lowest to highest energy level.
• fill orbitals within the same sublevel one at a time, before pairing the electrons.
Equation for electrons in each energy level
2n^2
N= energy level
Aufbau Principle
Electrons fill orbitals from the lowest-energy upward
Pauli’s Exclusion
Each orbital can hold only two electrons, which must be of opposite spin
Hund’s Rule
Two or more orbitals with the same energy are each half-filled by one electron before any one orbital is completely filled
The number of electrons in each subshell is indicated by
The superscript
Lewis Electron-dot symbol
Atomic symbol with dots placed around it to indicate the number of valence electrons
Dalton’s atomic theory
- All matter is made of atoms. Atoms are indivisible and indestructible.
- All atoms of a given element are identical in mass and properties
- Compounds are formed by a combination of two or more different kinds of atoms.
- A chemical reaction is a rearrangement of atoms.
Modern atomic theory
- All matter is composed of atoms.
- The atoms of a given element differ from the atoms of all other elements.
- Chemical compounds consist of atoms combined in specific ratios. Only whole atoms can combine.
- Chemical reactions change only the way atoms are combined in compounds.
The discovery of the electrons during a cathode experiment, proved that the atom wasn’t indivisible since the atom had even smaller units. Later the gold foil experiment gave us a better idea of how the sub particles are arranged.
Isotope symbols
A = mass number
Z = atomic number (# of p)
Electron affinity
Amount of energy released upon accepting an electron
Has to do with atoms ability to steal electrons from other atoms
The Bohr model of atoms
has individual energy levels from n=1 up to n=7.
The principal energy levels correspond to the periods on the periodic table
Quantum theory of electron configuration
principal energy levels are split into sublevels or subshells that group electrons based on the amount of energy they have.
Sublevels/subshells are organized into orbitals that are represented by three-dimensional shapes related to the probability of finding an electron within the sublevel based on the electron’s energy.
