✅2 - Bonding and Structure Flashcards
What is ionic bonding?
The strong electrostatic attraction between oppositely
charged ions
What effects does ionic radius have on the strength of ionic bonding?
The smaller the radius, the stronger the ionic bond
What effects do charges have on ionic bonding?
The greater the charge, the stronger the bond
How are ions formed?
By the loss (+) or gain (-) if electrons
What is a cation?
A positively charged ion
What is an anion?
A negatively charged ion
What does isoelectronic mean?
Two or more molecular entities that have the same number of electrons or a similar electron configuration
How does a positive charge affect atomic radius?
It gets smaller because it loses electrons from its outer shell
How does a negative charge affect ionic radius?
It gets larger because electrons are added to the outer shell
What are the trends in atomic radii for ions with different charges?
The larger the charge, the bigger the change in the ion’s size
How can the migration of ions be observed?
During electrolysis of coloured compounds
What does ionic migration prove?
The existence of ions
What are the melting/ boiling temperatures of ionic compounds like and why?
High becouse they have strong electrostatic forces between oppositely charged ions in their lattice structure, requiring large amounts of energy to break.
What are ionic compounds like physically?
They’re hard, brittle, crystalline substances
How soluble are ionic compounds?
They’re soluble in water and other polar solvents but insoluble in non polar solvents
Do ionic compounds conduct?
Not when solid, because their ions cannot move away from their fixed positions, but they do conduct when melted or dissolved
What happens when ions reach the anode?
They lose electrons
What happens when ions reach the cathode?
They gain electrons
What is a covalent bond?
The strong electrostatic attraction between two nuclei and the shared pairs of electrons between them
What is a dative covalent bond?
One in which both the electrons in the bonding pair are provided by one atom
What do lone pairs of electrons do?
- Affect the shapes of molecules
- Are used to form dative covalent bonds
- Are important in the chemical reactions of some compounds including water and ammonia
What is bond length?
The distance between the nuclei of two bonded atoms in a molecule
How can bond lengths be measured?
Using X-Ray diffraction when solid or Microwave spectroscopy when gaseous
What does bond length depend on?
The size of atoms involved and the number of pairs of electrons shared
Why do large atoms form longer bonds?
Because they have more electrons which shield the nuclei and reduce the attraction for the electron cloud.
Single bonds are…
…longer than double bonds, which are longer than triple bonds
Why are triple bonds shortest?
very strong attraction due to the greater electron density which pulls the 2 nuclei closer together
What is bond energy?
The energy required to break one mole of the bonds in a substance in the gaseous state
Which bonds have greater bond strength?
Sigma(single) bonds, they’re stronger and have greater bond energy.
What is the shape of a simple molecule or ion determined by?
The repulsion between the electron pairs that surround the central atom
What is electronegativity?
The ability of an atom to attract the bonding electrons in a covalent bond
Ionic and covalent bonds are the extremes of…
…a continuum of bonding type
Electronegativity differences lead to…
…bond polarity in bonds and molecules
What are the 3 most electronegative elements?
hint: think of (H bonds)
Nitrogen, Oxygen, Flourine
How do London Forces occur?
London forces occur due to temporary dipoles formed when electrons move unevenly around an atom or molecule
What is polarisability?
Describes how easily an atom/molecule’s electron cloud can be distorted.
Bigger molecules with a larger number of electrons have a…
…higher polarisability and potential for temporary dipoles
Why do the boiling temperatures rise down Group 7 and Group 0?
Because the atoms get bigger and have a greater polarisability and more electrons, so more London forces
Why do branched alkanes have lower boiling points?
Because the have a smaller surface area and therefore less poralisibility so less london forces are formed between them
What are the properties of simple molecular structures?
Usually gases, liquids or soft solids at room temperature
Have relatively low melting and boiling temperatures
Do not conduct electricity as thy contain neither ions or free electrons.
Usually soluble in non polar solvents
What is electron pair repulsion theory?
That electron pairs n the utter shell of atoms and ions repel each other and get as far away as possible
What is a bond angle?
The angle between who covalent bonds ina molecule or giant covalent structure
What does isoeletronic mean?
Molecules and ions that have exactly the same number and arrangement of electrons
What is the bond angle in a linear molecule?
180
What is the bond angle in a trigonal planar?
120
What is the bond angle in a tetrahedral molecule with no lone pairs?
109.5
What are the bond angles in trigonal bipyramidal molecules?
90, 120, 180
What are the bond angles in octahedral molecules?
90 and 180
Ammonia and water are isoelectronic with…
…methane
How are lone pairs held in relation to the central atom?
Closer than bonding pairs
What is the strength of repulsion between electron pairs?
Lone pair - lone pair > Lone pair - bonding pair > bonding pair - bonding pair
How do double or triple bonds affect shapes of molecules?
They don’t, they are treated as one bond and as a separate centre of negative charge
What are polar covalent bonds?
Bonds between atoms of different elements. The shared electrons are drawn towards the atom with the stronger pull on the electrons.
How does a big difference in electronegativity affect bonding type?
The bigger the difference in electronegativity, the more polar, and the more ionic a bond is.
How does electronegativity change down a group?
It decreases
Why is a polar liquid attracted to an object wth electrostatic charge?
Because polar molecules tend to move and rotate because the charge on one side of the molecule is attracted to the opposite charge of the object
What are the essential requirements for hydrogen bonding?
A hydrogen atom covalently bonded to a highly electronegative atom
A lone pair of electrons on a second electronegative atom
What is a saturated solution?
Contains as much of the solute as possible at a particular temperature
What are the interactions involved in solubility?
The intermolecular forces between solute molecules
The intermolecular forces between solvent molecules
The intermolecular forces between solute and solvent molecules
When does a molecular substance dissolve?
If the energy needed to break intermolecular forces and to separate the molecules in the solute and in the solvent is about the same as the energy released as the solute forms new intermolecular forces with the solvent
What is a non-aqueous solvent?
Any solvent other than water
What is hydration?
It takes place when water molecules bond to ions or add to molecules. Water molecules are polar o are attracted to both positive and negative ions
What are allotropes?
Different forms of the same element in the same physical state
What are the allotropes of carbon?
Diamond, graphite, fullerenes, graphemes
Why does Diamond not conduct electricity?
The electrons in the cola lent bonds are not delocalised
What are composites?
Two or metals combined to create a new material which has the desirable properties of both its constituents
What are delocalised electrons?
Bonding electrons not fixed in a bond between two atoms. Free to move around and shared by many atoms.
What is metallic bonding?
The strong electrostatic force of attraction between metal ions and delocalised electrons
