Chap 2 Flashcards
Graphite vs diamond
G: strong covalent bonds between carbon atoms in each layer, there are only weak forces between layers
Diamond: Each carbon atom is the same distance to each of its neighboring carbon atoms. rigid network
Atomic number
protons in the nucleus
Atomic mass
sum of protons and neutrons in the nucleus
What properties do valence electrons determine
Electrical § Optical
§ Thermal § Chemical
Bohr’s model
Bohr atomic model, in which electrons are assumed to revolve around the atomic nucleus in discrete orbitals, and the position of any particular electron is more or less well defined in terms of its orbital
wave-mechanical model
the electron is considered to exhibit both wave- like and particle-like characteristics.
e position is considered to be the probability of an electron being at various locations around the nucleus.
What do quantum numbers say
The size, shape, and spatial orientation of an electron’s probability density (or orbital) are specified by three of these quantum numbers.
principal quantum number n
Energy level
This quantum number is related to the size of an electron’s orbital
K L M N O
1, 2, 3, 4
second quantum number l
subshell. -> shape
Values of l are restricted by the magnitude of n and can take on integer values that range from l = 0 to l = (n − 1).
0, 1, 2, 3 -> s, p, d, f
Third quantum number m_l
ml can take on integer values between −l and +l, including 0
-> orientation
Fourth quantum number m_s
Spin moment
Associated with each electron is a spin moment, which must be oriented either up
or down.
+1/2 (for spin up) and −1/2 (for spin down)
Pauli exclusion principle
another quantum-mechanical concept, which stipulates that each electron state can hold no more than two electrons that must have opposite spins
stable electron configurations
The states within the outermost or valence electron shell are completely filled
Periodic table Groups:
Elements in the same column (group) share similar valence electron configurations and properties.
Trends Across Periods
Properties change systematically across each period moving horizontally.
Electronegativity:
Elements on the right side are electronegative, readily accepting electrons; electronegativity increases from left to right and bottom to top.
Periodic table metals
Metals: Most elements are classified as metals or electropositive, capable of giving up valence electrons.
Types of primary interatomic bonds
Ionic, covalent, metallic
Bonding Energy
Bonding energy is the energy needed to separate two atoms to infinite distance
Ionic bonding
compounds that are composed of both metallic and nonmetallic elements
Metallic elements easily transfer (give up) their valence electrons to the nonmetallic elements. In the process all the atoms acquire stable or inert gas configurations, and they become ions. Then the coulombic force (attractive) acts upon these two oppositely charge ions
Characteristics ionic material
Ionic bonding is nondirectional (i.e. the magnitude of the bond is equal in all directions around an ion). The bonding energy is relatively large
§ high melting temperature
§ hard and brittle
§ electrically and thermally insulative.
Covalent bonding who does it
nonmetallic molecules with similar (e.g., H2, F2) or dissimilar (e.g., CH4, HF) atoms and in elemental solids such as C and Si
Covalent bonding
Stable electron configuration achieved by sharing electrons between adjacent atoms in covalent bonds.
§ Covalently bonded atoms contribute at least one electron to the shared bond.
§ Covalent bonding is directional, occurring specifically between certain atoms.
§ Covalent bonding is very strong in nature.
§ Characteristics of covalently bonded materials:
- very hard (eg. C)
- very high melting temperature (>3550 oC for C)
*or can be very weak and has low melting temperature (eg. Bismuth, 270 oC).
