Lectures 1-4 Flashcards
The closer the electrons are to the nucleus, do they need more or less energy to leave the atom?
More energy they require to leave the atom
What is the first electron shell represent with?
1s
What is the second electron shell represented with?
2s, 2p
What is the third electron shell represented with?
3s, 3p …
What does the number to the power of the letter (s,p…) represent?
The number of electrons in that specific shell
Valency is?
the atoms ability to enter a combination with other elements. Also the number of electrons that the element gains/loses to get a full outer shell
Electropositive is?
What do they prefer to do?
Elements to the left of the period table.
Lose electrons
Electronegative is?
What do they prefer to do?
Elements to the right of the period table
Primary bonds
What happens to the electrons?
Strong chemical bonds
Shared or transferred
Secondary bonds
What happens to the electrons?
Weak interactions between atoms and/or molecules
Examples of primary bonding
Ionic, covalent, metallic
Examples of secondary bonding
Van der waals, hydrogen bonding
Ionic bonds are formed by…
electrons are transferred
Covalent bonds are formed by…
electrons being shared
Pros of metallic bonding
electrical conductivity, good tensile and compressive strength, high ductility
Van der waals forces, where do these occur?
Between atoms or molecules
What is the strength of van der waals forces?
Weak
What happens when an induced dipole is formed?
As two atoms get close to each other, the negative electrons and the positive nuclei are attracted to eachother, bringing the atoms together with a very small force.
Hydrogen bonding takes place where?
Between molecules that have H-F, H-N, and H-O bonds within them
In a potential energy and internuclear separation graph, what can we say if the curve is deeper?
More potential energy to break the bonds, bond is stronger
Coefficient of thermal expansion is?
How tolerant a material is towards heat
What do systems generally prefer to reach?
A minimum energy state or lower enthalpy
Crystalline structures are
atoms/molecules in a regular repeated form, usually solid
Examples of crystalline structures at room temp
metals and ceramics
Amorphous structures are
atoms/molecules in an irregular arrangement
Single crystal material is…
whole material has a consistent arrangement of atoms
Semi-crystalline material is…
crystalline regions and amorphous regions
Polycrystalline material is…
composed of many single crystal regions or grains that are oriented at random
Polymorphic materials can adopt more than one what?
More than one crystal structure
Allotropic structures are…
pure elements that can adopt different crysal structure depending on the different temperatures and pressures
Examples of crystal structures
NaCl sodium chloride, graphite and diamond
What does face centred cubic mean?
Circle faces showing on each side of the cube
What does body centred cubic mean?
The central sphere is contained in the centre of the cube
What does a hexagonal close packed structure look like?
Two hexagons forming a prism, with three additional atoms at equidistance from every atom forming a triangle
Vacancy in a material is
hole in the crystal of a material, absence of an atom
Dislocation in a material is
defects when half a row of atoms are missing from the crystalline layer and the surrounding layers of the crystal close in.
What is the pro to vacancy
Enable relative easy diffusion of atoms through a solid lattice
Yield stress is
the maximum amount of force a material can take before it is inelastically deformed
Tensile load is
force putting a material under tension
Shear stress is
forces being applied which slide the layers in a crystal along side eachother
Plastic deformation is when
the material becomes permanently deformed
Edge dislocation slip is when
a shear stress is applied to a structure with a dislocation and then the atoms below the dislocation break their bonds and slide along. Until the dislocation is then at one end of the crystal structure.
Dislocations in a material allow it to be
ductile
The presence of dislocations in a material allow the planes of atoms to…
slip past eachother at lower applied stresses
Ionic and covalent bonds are more what compared to metals
Brittle/less ductile
Slip is usually easier in the direction of the atoms where they are…
more closely packed
