PERIODIC TRENDS AND INTRAMOLECULAR FORCES Flashcards
Describe atomic mass
The mass of an atom of a chemical element expressed in atomic mass units. It is approximately equivalent to the number of protons and neutrons in the atom (the mass number) or to the average number allowing for the relative abundances of different isotopes
Describe mass number
The mass of protons and neutrons in a specific isotope of an element
Describe atomic number
Atomic number, the number of a chemical element in the periodic system, whereby the elements are arranged in order of increasing number of protons in the nucleus
Describe atomic weight
the average mass of an atom of an element as it occurs in nature that is expressed in atomic mass units.
Atomic weight =
(% abundance isotope 1/100) x (mass of isotope 1) +
(% abundance isotope 2/100) x (mass of isotope 2) + …
Define an isotope and how isotopes of the same element differ
An isotope is an atom with the same atomic number (number of protons) but different mass number, therefore a different number of neutrons. The notable difference of isotopes is their radioactivity. Often 1 isotope occurs more commonly, it is the most stable
Understand the purpose and structure of the periodic table
The chemical elements are arranged in order of increasing atomic number. The horizontal rows are called periods and the vertical columns are called groups. Elements in the same group have similar chemical properties.
In terms of periodic trends describe: metallic and non-metallic nature of the elements
Metallic character decreases diagonally right to left and increases diagonally left to right.
In terms of periodic trends describe: atomic radius
Atomic radius of an element decreases down a group and backwards along a period
1/2 the diameter of a neutral atom
Atomic size increases with the number of shells
the size of an atom is determined by the distribution of electrons around its nucleus. The closer the electrons are to the nucleus, the more tightly they are bound, thus increasing the electronegativity of the atom
In terms of periodic trends describe: effective nuclear charge
Zeff = Z (no. of protons) - S (number of shielding electrons)
The more shielding, the weaker the nucleus’ hold on the valence electrons, the greater the reactivity
Increases up a group and left to right across a period
In terms of periodic trends describe: number of valence electrons
Valence electrons increase left to right across a period
In terms of periodic trends describe: Ionisation energy
A measure of how difficult it is to remove the most loosely held electron from an atom in the gaseous phase
Largely based on Zeff
Ionisation energy increases left to right across a period and up a group
In terms of periodic trends describe: Ionic radius
Atomic is the distance away from the nucleus. Atomic radius increases going from top to bottom and decreases going across the periodic table. Ionic radius is the distance away from the central atom.
In terms of periodic trends describe: reactivity
The more shielding, the weaker the nucleus’ hold on the valence electrons, the greater the reactivity
In terms of periodic trends describe: reactivity
Reactivity decreases as you go from left to right across a period. The farther to the left and down the periodic chart you go, the easier it is for electrons to be given or taken away, resulting in higher reactivity
The more shielding, the weaker the nucleus’ hold on the valence electrons, the greater the reactivity
Describe the octet rule
The octet rule states that atoms tend to form compounds in ways that give them eight valence electrons and thus the electron configuration of a noble gas. One way is by sharing their valence electrons with other atoms (covalent bonding), the second way is by transferring valence electrons from one atom to another (ionic bonding).
Describe:
- An anion and how they are formed
- A cation and how they are formed
- An anion is an ion with a negative charge, formed by an atom gaining one or more electrons. They have IE and gain in size as they gain electrons
- A cation is a positively charged ion, formed by an atom giving away one or more of its electrons. They have low IE and get smaller as they lose electrons
What is ionic bonding? provide examples
Ionic bonding is when one atom (usually a metal) gives up electron(s) to another atom (usually a non-metal)
Ionic bonds most commonly form between a metal and a non metal and have an electronegativity difference greater than 1.9
What is metallic bonding? provide examples
Metallic bonding explain the characteristic of metals, metal atoms are surrounded by a ‘sea of electrons’ which are organised in a crystalline pattern
Bonding between positive metal ions and a sea of electrons is strong
Describe covalent bonding (single, double and triple bonds)
Covalent bonding is when an atom shares an electron pair with another atom
When compared to ionic compounds, covalent compounds usually have a lower melting and boiling point, and have less of a tendency to dissolve in water. Covalent compounds can be in a gas, liquid, or solid state and do not conduct electricity or heat well
Single bonds is the sharing of 2 electrons, double bone is the sharing of 4 electrons, and triple bond is the sharing of 6 electrons
Describe the polarity of bonds and compounds
Only when two atoms of the same element form a covalent bond are the shared electrons actually shared equally between the atoms. When atoms of different elements share electrons through covalent bonding, the electron will be drawn more toward the atom with the higher electronegativity resulting in a polar covalent bond
non-polar covalent bonds have an electronegativity difference of less than 0.5, polar covalent bonds have an electronegativity difference of 0.5-1.9, both are most likely to form between 2 non-metals or a non-metal and a metalloid
Ionic bonds have an electronegativity difference greater than 1.9 and most commonly form between a metal and a nonmetal
What is a coordinate covalent bond?
A covalent bond in which one of the atoms contributes both of the electrons in the shared pair.
