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)
