What is the periodic table of elements?
The periodic table of elements is a systematic way of arranging the chemical elements, based on their atomic number, electron configuration, and recurring chemical properties. Elements are ordered in rows, called periods, and columns, called groups.
- Who created the modern periodic table?
The modern periodic table was developed by Dmitri Mendeleev in 1869. He arranged the elements by atomic weight and proposed that the properties of elements are periodic functions of their atomic weights.
- What are periods in the periodic table?
Periods are the horizontal rows in the periodic table. The period number indicates the highest energy level occupied by an electron for the elements in that period.
- What are groups in the periodic table?
Groups are the vertical columns in the periodic table. Elements in the same group have the same number of electrons in their outer shell, or valence electrons, and therefore often have similar chemical properties.
- What is the significance of an element’s position in the periodic table?
An element’s position in the periodic table relates to its atomic structure. The period number indicates the highest energy level of an electron in the atom, and the group number relates to the number of valence electrons.
- How are the transition metals different from other elements in the periodic table?
Transition metals are distinguished by their ability to form several different positive ions, by losing different numbers of electrons. They also have a d sub-level, which can hold up to 10 electrons, that is partially filled in their ground state or in any of their oxidation states.
- What are lanthanides and actinides?
Lanthanides and actinides are two series of elements often placed below the main body of the periodic table. Lanthanides, from atomic numbers 57-71, have partially filled 4f sub-levels. Actinides, from atomic numbers 89-103, have partially filled 5f sub-levels.
- What are alkali metals and what are their general properties?
Alkali metals are the elements in group 1 of the periodic table. They are highly reactive, have one valence electron, and tend to lose this electron in reactions to form positive ions with a charge of +1. Alkali metals include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr).
- What are the noble gases and why are they generally unreactive?
Noble gases are the elements in group 18 of the periodic table. They are generally unreactive because they have full valence shells, which make them stable and less likely to react with other elements. Noble gases include helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn).
- What is the trend in atomic radius as you move across a period in the periodic table?
As you move from left to right across a period, the atomic radius generally decreases. This is because electrons are added to the same energy level while the nuclear charge increases, causing the electron cloud to be drawn closer to the nucleus.
- What is ionization energy and how does it change across the periodic table?
Ionization energy is the energy required to remove an electron from a gaseous atom or ion. It generally increases across a period from left to right due to increasing nuclear charge, and decreases down a group due to the increasing distance of the outermost electrons from the nucleus.
- What is electronegativity and how does it vary in the periodic table?
Electronegativity is a measure of how strongly an atom attracts the electrons in a chemical bond. It generally increases across a period from left to right and decreases down a group.
- Why do elements in the same group often share similar chemical properties?
Elements in the same group often share similar chemical properties because they have the same number of valence electrons. This determines how an atom can bond with other atoms and therefore its chemical behavior.
- Why are there two different numbering systems for groups in the periodic table?
There are two different numbering systems because of historical development of the periodic table. The older system used Roman numerals and letters to differentiate between main group and transition metals. The newer system numbers groups from 1 to 18 sequentially from left to right.
- What is the ‘periodic law’?
The periodic law states that when elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties. This periodicity is seen in trends and patterns observed in the periodic table.
- What are the metalloids and where are they located in the periodic table?
Metalloids are elements that have properties of both metals and non-metals. They are located along the staircase-like line that separates metals and non-metals in the periodic table. Metalloids include boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te), and polonium (Po).
- How does electron affinity vary across the periodic table?
Electron affinity is the energy change associated with the addition of an electron to a gaseous atom. It generally increases across a period from left to right and decreases down a group.
- What are the halogens and what are their general properties?
Halogens are the elements in group 17 of the periodic table. They are highly reactive non-metals with seven valence electrons. Halogens readily gain one electron to achieve a full outer shell, forming ions with a charge of -1. Halogens include fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At).
- What does it mean for an element to be ‘synthetic’ or ‘man-made’?
A synthetic or man-made element is one that does not occur naturally and is produced artificially in a laboratory. These elements, often found at the bottom of the periodic table, are usually unstable and rapidly decay into lighter, more stable elements.
- What is the ‘block’ concept in the periodic table?
The ‘block’ concept refers to the division of the periodic table into s-, p-, d-, and f-blocks. This is based on the electron configuration of the elements: the type of orbital that is being filled in the outermost shell determines the block to which an element belongs.