Chemistry: Periodic Trends

Atomic Size

Electron cloud doesn’t have a definite edge, measure more than 1 atom at a time, and measure the atomic radius. This is half the distance between the 2 nuclei of a diatomic molecule

Three factors that influence periodic trends

Nuclear charge, energy levels, and shielding.  Energy levels + shielding affect groups. Nuclear charge affects periods

Three factors that influence periodic trends: Nuclear Charge

the more charge (protons), the greater the attraction between protons and electrons (+ and - attract). pulls electrons in closer

Three factors that influence periodic trends: Energy Levels

The higher energy level (the greater distance from the nucleus), the weaker the force of attraction

Three factors that influence periodic trends: Shielding

the inner electrons shield the valence electrons (blocking affect), weakening the attraction between nucleus and electrons.

Atomic Radius: Group Trends

As we increase the atomic number (go down a group). Each atom adds a energy level, valence electrons are shielded, and atoms get bigger as electrons can move farther out. Nucleus has a weaker pull/force 

Atomic Radius: Period Trends

Going from left to right, atoms get smaller, electrons are in the same energy level, and shielding is constant. More nuclear charge means that the outermost electrons are pulled closer (smaller atomic radius).

Ions

an atom (or group of atoms) that has a positive or negative charge. Positive and negative ions are formed when electrons are transferred (lost or gained) between atoms

Cation

Losing electrons creates a positively charged particle. Metals tend to lose electrons from their outer energy level. The naming of a cation is the element name + ion.

Configuration of cations

Ions always have a noble gas configuration (a full outer level). Metals form ions with the configuration of the noble gas before them on the periodic table

Anion

gaining electrons, creating a negatively charged particle. Non-metals tend to gain electrons. The naming of an anion is when you add “ide” to the end of the element name.

Configuration of anions

Non-metals end up with the configuration of the noble gas after them

Trends in Ionic size: Anions

Anions are bigger than the atom they came from. Have the same energy level but a greater area the nuclear charge needs to cover. More electron repulsion makes a bigger cloud 

Trends in Ionic size: Cations

Cations are smaller than the atom they came from. Lose an entire energy level

Size of Isoelectronic Ions

“Iso” means the same. Isoelectronic ions have the same # of electrons and have the same configuration. However they have a different amount of protons. Ex: Ne, and O-2

Ionization energy

The amount of energy needed to completely remove an electron  

First Ionization energy

The energy required to remove only the first electronics called the first ionization energy. Removing one electron makes a 1+ ion

Second Ionization energy 

Second ionization energy is the energy needed to remove the second electron. Always more energy than the first ionization energy. For elements that reach a half-filled or filled orbitals, it removes 2 electrons

Third Ionization energy

Third ionization energy is the energy required to remove a third electron. Always greater IE than the first and second. Atoms in the aluminium family form 3+ ions

Factors that affect Ionization Energy

Nuclear charge: a higher nuclear charge needs more IE.

Atomic size: the bigger the atomic size, the less IE because the distance between the nucleus and the valence electrons grows.

Shielding: The more shielding means the less nuclear energy felt by the valence electrons, which lessens IE.

Electron configuration: Half-filled and filled orbitals are more stable, which makes them less willing to give up electrons. This makes the IE needed very high.

Shielding

The electron on the outermost energy level has to look through all the other energy levels to see the nucleus. Second electron has the same shielding if it is in the same period.

Ionization energy: Group Trends

As you go down a group, the first IE decreases. Electrons are farther away from the nucleus, which makes for less attraction and more shielding.

Ionization energy: Period Trends

All the atoms in the same period have the same energy level + shielding. Increasing nuclear charge. IE generally increases from left to right. There are Exceptions at full and ½ full orbitals 

Driving force for these changes of ionization energy

Full energy levels require a lot of energy to remove their electrons. Noble gases have full orbitals. Atoms behave in ways to try and achieve a noble gas configuration 

Covalent bonds

When non-metals react together, they need to gain electrons to fill their outer shell and become stable. They do this by sharing electrons with each other.

Electronegativity

The tendency for an atom to attract electrons to itself when it is chemically combined with another element. Atoms with large electronegativities strongly pull electrons towards themselves 

Bond types

Equal distribution, unequal distribution, and separate electron cloud

Bond types: Equal distribution

nonpolar covalent

Bond types: unequal distribution

polar covalent bonds

Bond types: Separate electron cloud

ionic

Electronegativity: Group Trends

The further down a group, the father the electron is from the nucleus. Also has more electrons, which makes it more willing to give them away. Electronegativity decreases as you go down groups 

Electronegativity: Period Trends

Metals let their electrons go easily, with lower electronegativity. Non-metals want more electrons as they are on the right side.Therefore, across a period, electronegativity increases