Helium is classified as a noble gas because its valence electron shell is complete, making it chemically inert. Noble gases are known for their lack of reactivity.

Atomic radius decreases across a period due to the increased effective nuclear charge drawing electrons closer to the nucleus. This is a fundamental periodic trend observed in the periodic table.

Atomic radius increases down a group because new electron shells are added, which increases the distance between the nucleus and the outer electrons. This trend overrides the slight increase in effective nuclear charge.

Elements are arranged by increasing atomic number, which ensures that periodic patterns in chemical properties are maintained. This order reflects the structure of the atom more accurately than atomic mass.

Lithium is the lightest metal on the periodic table due to its low atomic mass and its position in the alkali metals group. Its small size and low density are key characteristics distinguishing it from other metals.

Fluorine is the most electronegative element because it has a strong tendency to attract electrons in a chemical bond. Its high electronegativity is due to its small atomic size and high effective nuclear charge.

Sodium is found in period 3 and group 1, identifying it as an alkali metal. Its position in the periodic table helps explain its properties, such as high reactivity and a single valence electron.

Alkaline earth metals typically form +2 ions by losing two electrons. This divalent nature is a key characteristic of the group and influences their chemical behaviors and compound formation.

Copper is renowned for its excellent electrical conductivity, making it a prime choice for wiring and electronic applications. Its classification as a transition metal also contributes to its unique set of physical properties.

Ionization energy increases across a period because the effective nuclear charge increases, binding electrons more tightly to the nucleus. As a result, more energy is required to remove an electron from an atom.

The given electron configuration corresponds to chlorine, which has seven electrons in its outer shell. This configuration underpins many of chlorine's chemical properties, including its high reactivity as a halogen.

Group 17 elements are known as halogens. They possess seven valence electrons which make them highly reactive and prone to gaining an electron to achieve a stable noble gas configuration.

Cesium is considered one of the most reactive alkali metals due to its large atomic size and low ionization energy. Its position at the bottom of group 1 contributes to its high reactivity in chemical reactions.

Tungsten is famous for its extremely high melting point, which makes it suitable for high-temperature applications. This characteristic stems from its strong metallic bonds and dense atomic structure.

As you move down a group, the atomic mass increases significantly while the added electron shells do not increase the volume proportionally. This results in a higher density for elements lower in the group.

Aluminum commonly forms a +3 oxidation state by losing its three valence electrons. Its electron configuration and position in the periodic table make this oxidation state the most stable for the element.

Potassium, being further down in the alkali metal group, has more electron shells than Lithium, Beryllium, or Carbon. This increase in the number of electron shells results in a larger atomic radius.

Neodymium is a lanthanide, part of the group of elements that fill the 4f orbital. Lanthanides share similar chemical properties and are often referred to as rare earth elements.

Lithium and magnesium exhibit a diagonal relationship because their similar charge densities result in comparable chemical behaviors. Despite being in different groups, the small size of lithium and the comparable properties of magnesium lead to these similarities.

Ionization energy decreases down a group because additional electron shells increase electron shielding, reducing the effective nuclear pull on outer electrons. This trend makes it easier to remove an electron from an atom lower in the group.