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Chemistry topic 3 + 13 - Coggle Diagram
Chemistry topic 3 + 13
3.1 The arrangement of elements in the periodic table helps to predict their electron configuration
Periodic table is arranged by increasing atomic number ( left - right)
The blocks refer to the elements who contain electrons in those outer levels ( 2p = valence electrons in the 2p level)
Elements within the same
period
contain valence electrons in the same outer energy shell (principal energy level)
Elements in the same
groups
have the same number of valence electrons in their outer shell and have similar chemical reactivities
Shows the position of metals, non-metals and metalloids
Metals: lose electrons to form cations
Non-metals: gain electrons to form anions
Metalloids: properties of metals and non-metals
3.2 Elements show trends in their physical and chemical properties across periods and down groups
Periodicity
Trends in the physical and chemical properties of elements based on their position on the periodic table and can usually be explained by effective nuclear charge of an element
Effective nuclear charge
The overall attraction that the electrons have to the nucleus after the effect is reduced by repulsions and shielding by other electrons
Is less than nuclear charge due to repulsions and shielding
Decreases down a group due to shielding
Increases across a period due to the extra attraction from added protons are stronger than the extra repulsion from the added electrons
Atomic radius
Half the distance between two bonded atom's nuclei of an element
-Decreases across a period (as effective nuclear charge increases) due to the greater attraction of the other electrons to the protons in the nucleus
-Increases down a group due to greater shielding and electrons are further away from the nucleus
Ionic radius
The distance from the nucleus of an ion to the outermost electrons of an ion
-Decreases as effective nuclear charge increases due to more attraction to the nucleus
-Decreases across a period due to either more electrons being donated or less electrons being accepted (both lead to stronger attractions to the nucleus)
There is a large jump from metals to non-metals due to the switch from donating to accepting (group 5 will accept more electrons than group 7)
-Is larger than atomic radius in anions due to the increased electron repulses
-Is smaller than atomic radius in cations due to the decreased electron pulses
Ionization energy
The energy required to remove 1 mole of electrons from 1 mole of gaseous atoms and produce 1 mole of cations
-Decreases down a group due to increased shielding
-Increases across a period due to increased attraction to the nucleus (added protons)
EXCEPTIONS
Decrease in Be (1s2 2s2) - B (1s2 2s2 2p1): the 2p1 electron is more shielded than the 2s2 electrons (same for magnesium and aluminium)
Decrease in N ( 1s2 2s2 2p3) - O (1s2 2s2 2p4): in oxygen, 2 electrons occupy the same orbital and experience more repulsion (think about orbital boxes) paired = easier than unpaired (same for Phosphorus and sulfur)
Electron affinity
The change in energy that occurs when 1 mole of electrons is added to 1 mole of neutral atoms in the gaseous state
-Is a negative value (energy released)
-Increases across a period due to increase in effective nuclear charge
Think of it this way: the more you move across a period, the more an element will want to gain an electron to have a full shell. group 7 will want it more than group 5
Electronegativity
An atoms ability to attract a shared pair of electrons in a covalent bond
-Decreases down a group due to shielding
-Increases across a period due to increase in effective nuclear charge
Trends in Alkali metals
Are very reactive
Have low ionization energies (easily form 1+ cations)
increase in reactivity down a group
react with water to form hydroxide salts and H2
-2M(s) + 2H2O(l) -> 2MOH + H2
React with halogens to produce halide salts
-2M + X2 -> 2MX(s)
Trends in halogens
Exist as diatomic molecules (X2)
High electron affinities (easily become 1- anions)
F + Cl = Yellow
Br = brown
I = purple
undergo displacement reactions (more electronegative halogen will replace a less electronegative halogen)
-X2 + 2Y- -> 2X- + Y2
Trends in metals
Have low ionization energies and low electronegativities (lose electrons easily)
Have high conductivity as their electrons are not held to single atoms in solids and move around
Trends in non-metals
Have high ionization energies, electronegativities and electron affinities
Do not conduct electricity as their electrons are held in covalent bonds
Trends in metalloids
more similar to metals in physical properties
more similar to non-metals in chemical properties