The document provides information about the periodic table of elements and related concepts: 1) The periodic table arranges the chemical elements by atomic number and electron configuration, showing periodic trends in properties. Elements are grouped into blocks by their electron configurations and periods by the filling of electron shells. 2) Key concepts discussed include atomic number, electron configuration, chemical properties, periodic trends, metals, nonmetals, groups such as halogens and noble gases, periods, and shells and subshells. 3) Dmitri Mendeleev is credited with publishing the first recognizable periodic table in 1869, organizing known elements and predicting properties of undiscovered elements. His work established the basis for the modern periodic table

1. PERIODIC TABLE OF
ELEMENTS
GRADE 8 SCIENCE

3. Periodic table
• The periodic table, also known as the periodic table of elements, is a tabular
display of the chemical elements, which are arranged by atomic number, electron
configuration, and recurring chemical properties. The structure of the table
shows periodic trends.
• The seven rows of the table, called periods, generally have metals on the left
and nonmetals on the right.
• The columns, called groups, contain elements with similar chemical behaviours.
• Six groups have accepted names as well as assigned numbers: for example, group
17 elements are the halogens; and group 18 are the noble gases.
• Also displayed are four simple rectangular areas or blocks associated with the
filling of different atomic orbitals.

4. Chemical element
•A chemical element is a species of atom having the
same number of protons in its atomic nuclei (that
is, the same atomic number, or Z).
• For example, the atomic number of oxygen is 8, so
the element oxygen describes all atoms which have
8 protons.

5. Atomic number
• The atomic number or proton number (symbol Z) of
a chemical element is the number of protons found in
the nucleus of every atom of that element.
• The atomic number uniquely identifies a chemical
element. It is identical to the charge number of the
nucleus.
• In an uncharged atom, the atomic number is also equal to
the number of electrons.

6. Electron configuration
• In atomic physics and quantum chemistry,
the electron configuration is the distribution
of electrons of an atom or molecule (or other
physical structure) in atomic or molecular
orbitals.
• For example, the electron configuration of
the neon atom is 1s2 2s2 2p6, using the notation
explained below.

7. Chemical property
• A chemical property is any of a material's properties that becomes
evident during, or after, a chemical reaction; that is, any quality that
can be established only by changing a substance's chemical identity.
• Simply speaking, chemical properties cannot be determined just by
viewing or touching the substance; the substance's internal
structure must be affected greatly for its chemical properties to be
investigated.
• When a substance goes under a chemical reaction, the properties will
change drastically, resulting in chemical change.
• However, a catalytic property would also be a chemical property.

8. Periodic trends
• Periodic trends are specific patterns in the properties
of chemical elements that are revealed in the periodic
table of elements.
• Major periodic trends include electronegativity, ionization
energy, electron affinity, atomic radii, ionic
radius, metallic character, and chemical reactivity.

9. A period
• A period in the periodic table is a row of chemical elements.
All elements in a row have the same number of electron shells.
• Each next element in a period has one more proton and is
less metallic than its predecessor.
• Arranged this way, groups of elements in the same column have
similar chemical and physical properties, reflecting the periodic law.
• For example, the halogens lie in the second-last column (group 17)
and share similar properties, such as high reactivity and the tendency
to gain one electron to arrive at a noble-gas electronic configuration
As of 2016, a total of 118 elements have been discovered and
confirmed.

10. Metal
• A metal (from Greek μέταλλον métallon, "mine, quarry,
metal") is a material that, when freshly prepared, polished,
or fractured, shows a lustrous appearance, and
conducts electricity and heat relatively well.
• Metals are typically malleable (they can be hammered into
thin sheets) or ductile (can be drawn into wires).
• A metal may be a chemical element such as iron;
an alloy such as stainless steel; or a molecular compound
such as polymeric sulfur nitride.

11. Nonmetal
• In chemistry, a nonmetal (or non-metal) is a chemical element that mostly lacks the
characteristics of a metal.
• Physically, a nonmetal tends to have a relatively low melting point, boiling point,
and density.
• A nonmetal is typically brittle when solid and usually has poor thermal
conductivity and electrical conductivity.
• Chemically, nonmetals tend to have relatively high ionization energy, electron affinity,
and electronegativity.
• They gain or share electrons when they react with other elements and chemical
compounds.
• Seventeen elements are generally classified as nonmetals: most are gases (hydrogen,
helium, nitrogen, oxygen, fluorine, neon, chlorine, argon, krypton, xenon and radon);
one is a liquid (bromine); and a few are solids (carbon, phosphorus, sulfur, selenium, and
iodine).
• Metalloids such as boron, silicon, and germanium are sometimes counted as nonmetals.

12. Group
• In chemistry, a group (also known as a family[1]) is a column
of elements in the periodic table of the chemical elements.
• There are 18 numbered groups in the periodic table; the f-
block columns (between groups 3 and 4) are not numbered.
• The elements in a group have similar physical or chemical
characteristics of the outermost electron shells of their
atoms (i.e., the same core charge), because most chemical
properties are dominated by the orbital location of the
outermost electron.

13. Halogens
• The halogens (/ˈhælədʒən, ˈheɪ-, -loʊ-, -ˌdʒɛn/) are
a group in the periodic table consisting of five chemically
related elements: fluorine (F), chlorine (Cl), bromine (Br), io
dine (I), and astatine (At).
• The artificially created element 117, tennessine (Ts), may
also be a halogen.
• In the modern IUPAC nomenclature, this group is known
as group 17.

14. Noble gases
• The noble gases (historically also the inert gases; sometimes referred
to as aerogens) make up a group of chemical elements with similar
properties; under standard conditions, they are all odorless,
colorless, monatomic gases with very low chemical reactivity.
• The six naturally occurring noble gases
are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and
the radioactive radon (Rn).
• Oganesson (Og) is variously predicted to be a noble gas as well or to
break the trend due to relativistic effects; its chemistry has not yet
been investigated.

15. Block
• A block of the periodic table is a set of elements
unified by the orbitals their valence electrons or
vacancies lie in.
• The term appears to have been first used
by Charles Janet.
• Each block is named after its characteristic
orbital: s-block, p-block, d-block, and f-block.

16. Atomic orbital
• In atomic theory and quantum mechanics, an atomic orbital is
a mathematical function that describes the wave-like behavior of
either one electron or a pair of electrons in an atom.
• This function can be used to calculate the probability of finding
any electron of an atom in any specific region around the atom's
nucleus.
• The term atomic orbital may also refer to the physical region or
space where the electron can be calculated to be present, as
predicted by the particular mathematical form of the orbital.

17. Periodic table
• The elements from atomic numbers 1 (hydrogen) through 118 (oganesson) have
been discovered or synthesized, completing seven full rows of the periodic table.
• The first 94 elements, hydrogen through plutonium, all occur naturally, though
some are found only in trace amounts and a few were discovered in nature only
after having first been synthesized.
• Elements 95 to 118 have only been synthesized in laboratories or nuclear
reactors.
• The synthesis of elements having higher atomic numbers is currently being
pursued: these elements would begin an eighth row, and theoretical work has
been done to suggest possible candidates for this extension.
• Numerous synthetic radioisotopes of naturally occurring elements have also been
produced in laboratories.

18. Periodic table
• The organization of the periodic table can be used to derive relationships between the
various element properties, and also to predict chemical properties and behaviours of
undiscovered or newly synthesized elements.
• Russian chemist Dmitri Mendeleev published the first recognizable periodic table in 1869,
developed mainly to illustrate periodic trends of the then-known elements.
• He also predicted some properties of unidentified elements that were expected to fill
gaps within the table. Most of his forecasts proved to be correct.
• Mendeleev's idea has been slowly expanded and refined with the discovery or synthesis of
further new elements and the development of new theoretical models to explain
chemical behaviour.
• The modern periodic table now provides a useful framework for analyzing chemical
reactions, and continues to be widely used in chemistry, nuclear physics and other
sciences.
• Some discussion remains ongoing regarding the placement and categorisation of specific
elements, the future extension and limits of the table, and whether there is an optimal
form of the table.

19. Dmitri Ivanovich Mendeleev
• Dmitri Ivanovich Mendeleev (often romanized
as Mendeleyev or Mendeleef)
• 8 February 1834 – 2 February 1907 [OS 27 January 1834 – 20 January 1907]) was
a Russian chemist and inventor.
• He is best remembered for formulating the Periodic Law and creating a
farsighted version of the periodic table of elements.
• He used the Periodic Law not only to correct the then-accepted
properties of some known elements, such as the valence and atomic
weight of uranium, but also to predict the properties of eight elements
that were yet to be discovered.

20. Electron configuration
• The electron configuration or organisation of electrons orbiting neutral atoms
shows a recurring pattern or periodicity.
• The electrons occupy a series of electron shells (numbered 1, 2, and so on).
• Each shell consists of one or more subshells (named s, p, d, f and g).
• As atomic number increases, electrons progressively fill these shells and subshells
more or less according to the Madelung rule or energy ordering rule, as shown in
the diagram. The electron configuration for neon, for example, is 1s2 2s2 2p6.
• With an atomic number of ten, neon has two electrons in the first shell, and
eight electrons in the second shell; there are two electrons in the s subshell and
six in the p subshell.
• In periodic table terms, the first time an electron occupies a new shell
corresponds to the start of each new period, these positions being occupied
by hydrogen and the alkali metals.[34][35]

21. Electron shell
• In chemistry and atomic physics, an electron shell, or
a principal energy level, may be thought of as
an orbit followed by electrons around an atom's nucleus.
• The closest shell to the nucleus is called the "1 shell" (also
called the "K shell"), followed by the "2 shell" (or "L shell"),
then the "3 shell" (or "M shell"), and so on farther and farther
from the nucleus.
• The shells correspond to the principal quantum numbers (n =
1, 2, 3, 4 ...) or are labeled alphabetically with the letters
used in X-ray notation (K, L, M, …).

22. electron shell
• Each shell can contain only a fixed number of electrons: The first shell can hold
up to two electrons, the second shell can hold up to eight (2 + 6) electrons, the
third shell can hold up to 18 (2 + 6 + 10) and so on.
• The general formula is that the nth shell can in principle hold up to 2(n2)
electrons.
• Since electrons are electrically attracted to the nucleus, an atom's electrons will
generally occupy outer shells only if the more inner shells have already been
completely filled by other electrons.
• However, this is not a strict requirement: atoms may have two or even three
incomplete outer shells. (See Madelung rule for more details.)
• For an explanation of why electrons exist in these shells see electron
configuration.

23. Electron shell
•The electrons in the outermost occupied
shell (or shells) determine the chemical
properties of the atom; it is called
the valence shell.
•Each shell consists of one or more subshells,
and each subshell consists of one or
more atomic orbitals.

24. Subshells
• Each shell is composed of one or more subshells, which are
themselves composed of atomic orbitals.
• For example, the first (K) shell has one subshell, called 1s;
the second (L) shell has two subshells, called 2s and 2p; the
third shell has 3s, 3p, and 3d; the fourth shell
has 4s, 4p, 4d and 4f; the fifth shell has 5s, 5p, 5d,
and 5f and can theoretically hold more in the 5g subshell
that is not occupied in the ground-state electron
configuration of any known element.

25. Electron configuration
• Since the properties of an element are mostly determined by its
electron configuration, the properties of the elements likewise show
recurring patterns or periodic behaviour, some examples of which are
shown in the diagrams below for atomic radii, ionization energy and
electron affinity.
• It is this periodicity of properties, manifestations of which were
noticed well before the underlying theory was developed, that led to
the establishment of the periodic law (the properties of the elements
recur at varying intervals) and the formulation of the first periodic
tables.