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The periodic table

The different elements are organized and displayed in the periodic table    . Devised by Russian chemist Dmitri Mendeleev (1834–1907) in 1869, the table groups elements that, although unique, share certain chemical properties with other elements. The properties of elements are responsible for their physical state at room temperature: they may be gases, solids, or liquids. Elements also have specific chemical reactivity    , the ability to combine and to chemically bond with each other.

In the periodic table, shown in [link] , the elements are organized and displayed according to their atomic number and are arranged in a series of rows and columns based on shared chemical and physical properties. In addition to providing the atomic number for each element, the periodic table also displays the element’s atomic mass. Looking at carbon, for example, its symbol (C) and name appear, as well as its atomic number of six (in the upper left-hand corner) and its atomic mass of 12.11.

The periodic table consists of eighteen groups and seven periods. Two additional rows of elements, known as the lanthanides and actinides, are placed beneath the main table. The lanthanides include elements 57 through 71 and belong in period seven between groups three and four. The actinides include elements 89 through 98 and belong in period eight between the same groups. These elements are placed separately to make the table more compact. For each element, the name, atomic symbol, atomic number, and atomic mass are provided. The atomic number is a whole number that represents the number of protons. The atomic mass, which is the average mass of different isotopes, is estimated to two decimal places. For example, hydrogen has the atomic symbol H, the atomic number 1, and an atomic mass of 1.01. The atomic mass is always larger that the atomic number. For most small elements, the atomic mass is approximately double the atomic number as the number of protons and neutrons is about equal. The elements are divided into three categories: metals, nonmetals and metalloids. These form a diagonal line from period two, group thirteen to period seven, group sixteen. All elements to the left of the metalloids are metals, and all elements to the right are nonmetals.
The periodic table shows the atomic mass and atomic number of each element. The atomic number appears above the symbol for the element and the approximate atomic mass appears below it.

The periodic table groups elements according to chemical properties. The differences in chemical reactivity between the elements are based on the number and spatial distribution of an atom’s electrons. Atoms that chemically react and bond to each other form molecules. Molecules are simply two or more atoms chemically bonded together. Logically, when two atoms chemically bond to form a molecule, their electrons, which form the outermost region of each atom, come together first as the atoms form a chemical bond.

Electron shells and the bohr model

It should be stressed that there is a connection between the number of protons in an element, the atomic number that distinguishes one element from another, and the number of electrons it has. In all electrically neutral atoms, the number of electrons is the same as the number of protons. Thus, each element, at least when electrically neutral, has a characteristic number of electrons equal to its atomic number.

An early model of the atom was developed in 1913 by Danish scientist Niels Bohr (1885–1962). The Bohr model shows the atom as a central nucleus containing protons and neutrons, with the electrons in circular orbitals at specific distances from the nucleus, as illustrated in [link] . These orbits form electron shells or energy levels, which are a way of visualizing the number of electrons in the outermost shells. These energy levels are designated by a number and the symbol “n.” For example, 1n represents the first energy level located closest to the nucleus.

Three concentric circles around the nucleus of a hydrogen atom represent principal shells. These are named 1n, 2n, and 3n in order of increasing distance from the nucleus. An electron orbits in the shell closest to the nucleus, 1n.
The Bohr model was developed by Niels Bohrs in 1913. In this model, electrons exist within principal shells. An electron normally exists in the lowest energy shell available, which is the one closest to the nucleus. Energy from a photon of light can bump it up to a higher energy shell, but this situation is unstable, and the electron quickly decays back to the ground state. In the process, a photon of light is released.

Questions & Answers

What is Catabolism
Zanga Reply
Catabolism is a biochemical reaction that breaks large molecules into smaller ones
Araba
what is the roll of bile sait in digestive
Nadia Reply
what is the life cycle of a mosquito
Clara Reply
what is a organisms
Ronald Reply
consist of both plants and animals
Kingsley
what is animal hospitality
Marie Reply
what is a virus?
Yazi Reply
They are Akaryotes,they are made up of nucleoprotien particle.They are composed. of DNA and RNA
Nana
what is cell
Sulayman
what is animal compost
Marie
it is a small infectious agent that replicate inside the body cell of the living organism.
Peter
A cell is a structural and functional basic unit of life
lilchris
I believe a virus is a frustrated not fully recovered fuzzy relative. aggravated .( in my opinion.)
Heidi
a cell is a tiny room with tiny micro roommates to inforce a structure in some pattern , in my opinion.
Heidi
animal compost is the compound digested and regenerated in to compounded cleaned solid matter . We may use it for soil and farming.
Heidi
describe the evolutionary history of birds
Mable Reply
synchondrosis and symphyses are?
Mable
synchondroses and symphyses are?
Mable
Describe how manuals digest (1) starch (2) proteins
Isaac Reply
what is biodiversity
Amos Reply
different living forms on earth
kanchan
is simply the variation in all forms of life
Nana
different types of plants,animals,fungi and other microorganisms..all constitute biological diversity
kanchan
What is the hardesr bone in our body
Rowena Reply
right and left femur
Mehtab
leg bone
Agbesi
Thigh bone
kanchan
skull
Nana
thigh bone
Desery
femur
Faith
femur
Amos
femur
Mable
femur
Kingsley
What is diffusion?
Ronke Reply
The movement of particles from the region of high concentration to the region of low concentration.
Saim
Can osmosis occur in a liquid?
Ronke
yes, osmosis occur mostly in liquid while diffusion mostly in gases
Faith
Thanks😉
Ronke
What is an isotopic solution?
Ronke
I mean isotonic i
Ronke
diffusion is the movement of molecules from a region of high concentration to a region of low concentration
Yazi
Explain the processes of digestion and absorption
Keyard Reply
I believe the compounds and layers of nutrients is processed through a two to four way channel , ' The feed, the composing infringed bashingment compelling distinguished despret hault 'it fills the peak before the in richment of the boiling acids there of digestion reaping an absorption either .
Heidi
.
Nicole
What is the function of palisade bundle .
Daniel Reply
the reproductive system of awoman
Mwakwe Reply
what is a nucleotide
Nowamani Reply
A compound consisting of a nucloside linked to a phosphate group
Peace
is the building block for DNA and RNA
Yazi

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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