Chapter 2 Flashcards
Bohr atomic model
An early atomic model in which electrons were assumed to revolve around the nucleus in discreet orbitals
Pauli exclusion principle
The postulate that for an individual atom, at most two electrons, which necessarily have opposite spins, can occupy the same state
Atomic mass unit (amu)
A measure of atomic mass, 1/12 the mass of an atom of 12C
Atomic number (Z)
For a chemical element, the number of protons within the atomic nucleus
Atomic weight (A)
The weighted average of the atomic masses of an atom’s naturally occurring isotopes. Can be in amu or mass per mole of atoms
Bonding energy
The energy required to separate two atoms that are chemically bonded to each other. Can be expressed on a per-atom basis or per mole of atoms
Coulombic force
A force between charged particles such as ions; the force is attractive when the particles are of opposite charge
Covalent bond
A primary interatomic bond that is formed by the sharing of electrons between neighboring atoms that have similar electronegativities. Normally s and p orbitals are involved. Have variable bond energies, are directional, and are found in semiconductors, ceramics, and polymer chains.
Dipole (electric)
A pair of equal and opposite electrical charges separated by a small distance
Electron configuration
For an atom, the manner in which possible electron states are filled with electrons
Electron state
One set of discrete, quantized energies that are allowed for electrons. In the atomic case, each state is specified by four atomic numbers
Electronegative
For an atom, having the tendency to accept valence electrons. Also used to describe nonmetallic elements
Electropositive
For an atom, having the tendency to release valence electrons. Also used to describe metallic elements
Ground state
A normally filled electron energy state from which an electron excitation may occur
Hydrogen bond
A strong secondary interatomic bond that exists between a bound hydrogen atom (its unscreened proton) and the electrons of adjacent atoms
Ionic bond
A coulombic interatomic bond that exists between two adjacent and oppositely charged ions that requires the transfer of electrons and a large difference in electronegativity. They have large bond energy, are nondirectional, and are found in ceramics.
Isotope
Atoms of the same element that have different atomic masses
Metallic bond
A primary interatomic bond involving the nondirectional sharing of nonlocalized valence electrons (sea of electrons) that are mutually shared by all the atoms in the metallic solid. Have variable bond energies, are nondirectional, and are found in metals.
Mole
The quantity of a substance corresponding to 6.022 * 10^23 atoms or molecules
Periodic table
The arrangement of the chemical elements with increasing atomic number according to the periodic variation in electron structure. Nonmetallic elements are positioned to the far right-hand side of the table
Polar molecule
A molecule in which there exists a permanent electric dipole moment by virtue of the asymmetrical distribution of positively and negatively charged regions
Primary bonds
Interatomic bonds that are relatively strong and for which bonding energies are relatively large. Types: ionic, covalent, metallic
Quantum mechanics
A branch of physics that deals with atomic and subatomic systems; it allows only discrete values of energy. By contrast, for classical mechanics, continuous energy values are permissible
Quantum number
A set of four numbers, the values of which are used to label possible electron states. Three of the quantum numbers are integers that specify the size (n), shape (l), and spatial orientation (ml) of an electron’s probability density; the fourth number designates spin orientation (ms).
Secondary bond
Interatomic and intermolecular bonds that are relatively weak and for which bonding energies are relatively small. Normally, atomic or molecular dipoles are involved. Ex: van der Waals forces and hydrogen bonding. They are directional and either inter-chain (polymer) or inter-molecular.
Valence electron
The electrons in the outermost occupied electron shell, which participate in interatomic bonding and they tend to determine an atom’s chemical properties
Van der Waals bond
A secondary interatomic bond between adjacent molecular dipoles with asymmetrical electron fields that may be permanent or induced
Wave-mechanical model
An atomic mode in which electrons are treated as being wavelike
What properties are determined by an atom’s electronic structure?
- Chemical
- Electrical
- Thermal
- Optical
What are the number of states and electrons in s,p,d, and f subshells?
s: 1 state 2 electrons
p: 3 states 6 electrons
d: 5 states 10 electrons
f: 7 states 14 electrons
When are electron configurations stable?
When their electron states/orbitals are full
Why are filled energy shells more stable?
They require more energy to gain or lose atoms
What trend does atomic radius follow?
Increases from right to left and top to bottom on the periodic table
What trend do ionization energy and electronegativity follow?
Increases from left to right and bottom to top
What is the most common mixed bonding type?
Covalent-Ionic
How do melting point, elastic modulus, and thermal expansion relate to bond energy?
Melting point and elastic modulus increase (becomes stiffer) as bond energy increases and thermal expansion decreases
What is the most common bonding type for ceramics?
Ionic bonding
What are some characteristics of covalent bonds?
- Strong bonds
- High melting points
- Directional (atoms form chains to get the right bonding angle/direction)
- Common in polymers (formation of chains)
Why do polymers have low melting points?
Polymers have Van der Waals bonds between their polymer chains, which are weak bonds
What is the relationship between bond energy and thermal expansion?
A higher bond energy correlates with lower thermal expansion. The bonds resist the expansion
What type of bonds are found in ceramics?
Ionic and covalent bonding
- High bond energy
- High melting points
- Low thermal expansion
What types of bonds are found in metals?
Metallic bonds
- Moderate bond energy
- Moderate melting points
- Moderate thermal expansion
What type of bonds are found in polymers?
Covalent and secondary bonds
- Low bond energy
- Low melting points
- High thermal expansion
What properties are determined by electron structure?
- Chemical
- Electrical
- Thermal
- Optical
What does the percent ionic character of a mixed covalent-ionic bond depend on?
Electronegativity
