What is the uses of argon?

• Argon is widely used as an inert gas to create an oxygen- and nitrogen-free environment for various heat-treating processes.  
• It is used for metal production, welding and metallurgy, lighting and in the automotive industry. 
• Argon is used for filling fluorescent and incandescent light bulbs. Argon does not react with the filament and prevents oxygen from corroding it.  
• In the welding and metal fabrication industry, argon is used to create an inert atmosphere between the surrounding air and liquid metal. The gas also prevents oxidation risks and minimizes smoke emissions. 
• Argon is used in the automotive industry to weld mufflers, frames and other auto parts. It also creates a nitrogen- and oxygen-free environment for the annealing process and is an important component of airbags. The tires of some luxury vehicles contain argon to reduce road noise and protect the rubber.  
• In metal production, argon is used to create a non-reactive blanket during the manufacture of titanium and other reactive elements and as a protective environment for growing germanium and silicon crystals. 

What is electron affinity?

Electron affinity reflects the ability of an atom to accept an electron. It is the energy change that occurs when an electron is added to a gaseous atom.

• These reactions tend to be exothermic (release energy) because an electron approaching a neutral atom experiences an attraction for the positively charged nucleus. 
• So the values of EA are generally negative. The higher (more negative) the EA, the more easily it accepts an electron. 
• The smaller the atom, the closer an added electron can approach the atomic nucleus and the more strongly it is attracted to the nucleus.  
• However, affinity does not always release energy. In some cases affinity requires energy.

How are the trends of atomic radius and ionization energy related? Explain in both groups and periods.

These trends are inverses of each other. As the size of the atom increases, the ionization energy (energy required to remove the electron) decreases because the electron being removed is farther from the nucleus in a larger atom.Less energy is required to remove an electron further from the nucleus. [AR increases down a group while IE decreases; AR decreases across a period while IE increases.]

What’s the difference between electronegativity and ionization energy?

Electronegativity is related to the pull of a nucleus on an electron being shared in a bond. Ionization energy is the energy required to remove an electron from an unbonded atom. Electronegativity is a ranking and has no units. Ionization energy is an amount of energy and has units such as kilojoules.

Atomic Radius Trends

Why are atoms larger going down a group
Atoms get larger because the higher the energy level, the more orbitals it has and the further away from the nucleus those orbitals are. Also, more electrons are interfering with the attraction that the nucleus has on the highest energy electrons [shielding].

Why do atoms get smaller going from left to right across the table.
Atoms get smaller because there is an increase in the effective nuclear charge [more protons attracting more electrons) so the highest energy level get pulled in closer to the nucleus.

What are metalloids? State the properties of metalloids and list all the metalloids on the Periodic Table.

Metalloids are elements that lie along the zigzag line on the periodic table starting with Boron and moving down in steps. These elements share properties of both metals and non-metals. Metalloids are solids, ductile and malleable.  These are good semiconductors. At high temperatures metalloids acts like metals and conduct electricity. At lower temperatures metalloids act like nonmetals and stop electricity from flowing. This property is useful in electronic devices such as computers, tv's and solar cells. The metalloids include: Boron, Silicon, Germanium, Arsenic, Antimony, Tellurium, and Polonium.

Explain why the melting and boiling points of argon are higher than helium?

The atomic size of argon is bigger than helium. Thus, the forces of attraction between argon atoms are stronger than the forces of attraction between helium atoms. As a result, more heat energy is required to overcome the stronger forces of attraction between argon atoms. Hence, the melting and boiling points of argon are higher than helium.  

Why is helium gas used in airships while argon gas used in electric bulbs?

• Helium gas is suitable to fill airships because it is very light and non-flammable.
• Argon gas is suitable to use in electric bulbs because it is chemically inert. Hence, the hot tungsten filament in the electric bulb does not react with it. 

Describe the variation in melting points and electrical conductivities of the Period 3 elements from sodium to chlorine in terms of their structure and bonding.

Sodium, magnesium and aluminium have giant metallic structures with strong metallic bonds. They have relatively high melting point. Silicon has a giant covalent structure with strong covalent bonds. This accounts for its exceptionally high melting point. The rest are simple molecules with weak intermolecular van der Waals forces. The strength of the van der Waals force and the melting point increases in the order: Ar ˂ Cl₂ ˂ P₄ ˂ S₈. Sodium, magnesium and aluminium have mobile electrons. They are conductors. Silicon is a metalloid. The energy gap between the conduction band and the valence bond is small. It is a semi-conductor. Phosphorous, sulphur, chlorine and argon do not have mobile electrons. They are non-conductors.

Two factors that influence the changes of atomic radii in the Periodic Table

Two factors that influence the changes of atomic radii in the Periodic Table are:

• Effective nuclear charge experienced by the valence electrons: Electrons around the nucleus experience different nucleus attraction. Those electrons closer to the nucleus experience a greater attraction than those that are farther away. The actual nuclear charge experienced by an electron is called the effective nuclear charge, Z_eff. Effective nuclear charge increase, nucleus attraction stronger, atomic radii decrease. Across the period, the effective nuclear charge increases as proton number increase. As a result, the attraction between the nucleus and valence electrons become stronger, causing the atomic radius to decrease.
• The principal quantum number, n, of the valence electrons: As going down a group, the number of shells increases, more inner electrons are present to shield the valence electrons from the nucleus. The valence electrons are farther from the nucleus. Thus, the attraction between the nucleus and valence electrons decreases, therefore, the atomic radius increase. Down a group, the atomic radius increases because of the increasing principal quantum number (n) of the valence electron.

SPM Form 4: Periodic Table of elements (Checklist)

• Periodic Table: the table showing the elements in order of increasing proton number; similar elements are arranged in columns called groups.
• Group: A vertical column of elements in the Periodic table.
• Period: A horizontal row of the Periodic Table; its number tells you how many electron shells there are.
• Alkali metals: the Group I elements of the Periodic Table, which include lithium, sodium, potassium, rubidium, caesium and francium.
• Alkaline earth metals: the Group II elements of the Periodic Table, which include beryllium, magnesium, calcium, strontium, barium, and radium.
• Halogens: the Group VII elements of the Periodic Table, which include fluorine, chlorine, bromine, iodine and astatine.
• Noble gases: the Group 18 elements of the Periodic Table; they are called ‘noble’ or inert gases because they are so unreactive, which include helium, neon, argon, krypton, xenon and radon.
• Transition elements: the elements in the wide middle block of the Periodic Table (elements in group 3 to group 12).
• Metal: an element that shows metallic properties (for example conducts electricity, and forms positive ions)
• Non-metal - an element that does not show metallic properties: the non-metals lie to the right of the zig-zag line in the Periodic Table.
• Amphoteric oxide: An oxide that exhibits both acidic and basic properties.
• The atomic radius is a term used to describe the size of the atom.
• The ionization energy is the energy required to completely remove an electron from a gaseous atom or ion.
• Electron affinity reflects the ability of an atom to accept an electron. It is the energy change that occurs when an electron is added to a gaseous atom.
• Electronegativity is a measure of the attraction of an atom for the electrons in a chemical bond. The higher the electronegativity of an atom, the greater its attraction for bonding electrons.

Uses of the noble gases

The noble gases are unreactive or inert, which makes them safe to use. They also glow when a current is passed through them at low pressure. These properties lead to many uses:

• Helium is used to fill balloons and airships, because it is much lighter than air – and will not catch fire.
• Argon is used to provide an inert atmosphere. For example it is used: as filler in tungsten light bulbs and to protect metals that are being welded.
• Neon is used in advertising signs. It glows red, but the colour can be changed by mixing it with other gases.
• Krypton is used in lasers – for example for eye surgery – and in car headlamps.
• Xenon gives a light like bright daylight, but with a blue tinge. It is used in lighthouse lamps, lights for hospital operating rooms, and car headlamps.

Explain the reactivity of halogens decreases when going down Group 17.

The atomic size of halogen increases when going down Group 17. Thus, the outermost occupied shell becomes further away from the nucleus. Hence, the strength of the nucleus to pull another electron into the outermost occupied shell becomes weaker. Thus, halogens are less reactive when going down Group 17. 

Explain how the melting and boiling points change when going down the Group 1.

Melting and boiling points of alkali metals decreases when going down Group 1. The atomic size of alkali metals becomes bigger when going down the group 1. Hence, the forces between alkali metal atoms are weaker when going down Group 1. Hence, less heat energy is required to break the weaker forces.

Why noble gases chemically inert?

Helium has a duplet electron arrangement whereas other noble gases have octet electron arrangements. These electrons arrangements are very stable. Hence, atoms of noble gases do not release electrons, accept electrons or share electrons with other atoms. Thus, they are chemically inert. 

Why is neon exists as a monoatomic gas?

• Neon is from the Noble Gases group on the periodic table. 
• Neon has electron arrangement is 2.8 (valence electron is 8). 
• Neon already achieves the octet electron arrangement. 
• Neon does not need to donate the electron with other element. 
• Therefore they do not gain or lose electrons making them exist as individual atoms. 
• Neon exists as a monoatomic gas. 

Atomic Radius - trends on periodic table

Generally, the atomic radius decreases across a period from left to right and increases down a given group.

Moving from left to right across a period, electrons are added one at a time to the outer energy shell. Electrons within a shell cannot shield each other from the attraction to protons. Since the number of protons is also increasing, the effective nuclear charge increases across a period. This causes the atomic radius to decrease.

Moving down a group in the periodic table, the number of electrons and filled electron shells increases, but the number of valence electrons remains the same. The outermost electrons in a group are exposed to the same effective nuclear charge, but electrons are found farther from the nucleus as the number of filled energy shells increases. Therefore, the atomic radii increase.

Why does the atomic size decreases when going across Period 2?

When going across Period 2, the positive charge of the nucleus of the elements increases, atoms of elements in Period 2 have two shells occupied with electrons. Hence, the increasing positive charge of the nucleus pulls the two shells of electrons closer to the nucleus when going across Period 2. This causes the decreases in the atomic size.  

Why the boiling point of noble gases increases when going down the group?

The boiling point of noble gases increases when going down Group 18. This is because the atomic size of noble gases becomes bigger when going down Group 18. Thus, the forces of attraction between atoms become stronger when going down Group 18. More heat energy is required to overcome the forces between atoms. This causes the boiling point of noble gases to increases when going down Group 18. 

Predict the physical and chemical properties of astatine

Predict the physical and chemical properties of astatine. Astatine is placed below iodine in Group 17 of the Periodic Table.

 

Physical properties of astatine:

• Black solid
• Has low melting and boiling points
• Has a low density
• Cannot conduct electricity
• Poor conductor of heat
• Slightly soluble in water

Chemical properties of astatine:

• Astatine reacts with cold sodium hydroxide solution to form sodium astatide, sodium astatate (I) and water.

At_{2 (s)} + 2NaOH _(aq) → NaAt _(aq) + NaOAt _(aq) + H₂O _(l)

• Astatine vapour reacts with heated iron wool to form a brown solid of iron wool to form a brown solid of iron (III) astatide.

2Fe _(s) + 3At_{2 (g)} → 2FeAt_{3 (s)}