Periodic Table Trends

Flashcards about Periodic Table Trends

Atomic Radius

The distance from the centre of an atom to the valence orbital

Ionization Energy

Energy required to remove one electron from an atom or ion

Electron Affinity

The energy associated with adding an electron to the outer energy level of a neutral atom to form a negative ion

Electronegativity

The tendency of an atom to pull electrons towards itself in a bond

Reactivity

The rate at which a substance undergoes a chemical reaction

Dmitri Mendeleev's Periodic Table (1869)

Arranged elements by increasing atomic mass and was nominated for a Nobel Prize

Henry Moseley (1914)

Found that the pattern of the periodic table was due to atomic number, not atomic mass

Periodic Law

Many of the physical and chemical properties of the elements tend to appear at regular intervals with increasing atomic number

Trend

Predictable change in a particular direction

Electron Repulsion

Exists between the electrons of different energy levels because like charges repel

Effective Nuclear Charge

The charge felt by the valence electrons after taking into account the number of shielding electrons that surround the nucleus

Energy Level Influence on Atomic Radius

Electrons in a higher energy level are further away so there is decreased attraction

Charge on Nucleus Influence on Atomic Radius

More charge pulls electrons in closer, decreasing atomic radius

Shielding Effect Influence on Atomic Radius

E- to e- repulsion increases radius

Atomic Radius Trend Down a Group

As you go down a group, atomic radius increases because another energy level continues to be added, electrons are farther away from the nucleus, and there is less attraction between the electrons & the nucleus

Atomic Radius Trend Across a Period

As you go across a period, the radius decreases because electrons increase in number but are added to the same energy level, protons increase in the nucleus (more effective nuclear charge), and stronger attractive force pulls electrons closer to the nucleus

Anions

Larger than their neutral atom because electrons outnumber protons and repel one another, making the size of the ion larger

Cations

Smaller than their neutral atom because protons outnumber electrons and there are fewer energy levels

First Ionization Energy

The removal of the first electron from an atom

Ionization Energy Trend Down a Group

As you go down a group, electrons are further from the nucleus (easier to remove) and inner electrons shield the outside electrons from the positive nucleus

Ionization Energy Trend Across a Period

As you go across a period, atomic radius decreases (smaller atom) and proton number increases (higher effective nuclear charge, greater attraction to the nucleus)

Successive Ionization Energy

Each successive removal of an electron requires more energy

Non-metals

High electron affinity; they tend to form anions

Metals

Low electron affinities and tend to form cations

Negative electron affinity

If energy is released (exothermic)

Positive electron affinity

If the energy is absorbed (endothermic)

Electron Affinity Trend Down a Group

Decreases down a group because there is more electron shielding and less attraction for more electrons

Electron Affinity Trend Across a Period

Increases across a period because atomic radius decreases, electrons are closer to the nucleus, and there is more attraction

Electronegativity and Atomic Radius

If an atom has a small radius the electrons will be closer to the nucleus and experience a stronger pull

Metal Reactivity

Metals react by losing electrons, the easier it is to lose an electron, the more reactive a metal is

Metal Reactivity Trend Down a Group

Metal reactivity increases as you move down the periodic table

Metal Reactivity Trend Across a Period

Metal reactivity decreases as you move across the periodic table

Non-Metal Reactivity

Non-metals react by gaining electrons – the easier a non-metal gains electrons, the more reactive it is!

Non-Metal Reactivity Trend Down a Group

Non-metal reactivity decreases as you move down the periodic table

Non-Metal Reactivity Trend Across a Period

Non-metal reactivity increases as you move across the periodic table