1-An atom is the smallest constituent unit of ordinary matter that has the properties of a chemical element.
2-Every atom is composed of a nucleus and one or more electrons bound to the nucleus.
3-Every solid, liquid, gas, and plasma is composed of neutral or ionized atoms.
4-The nucleus is made of one or more protons and typically a similar number of neutrons.
5-Atoms are very small; typical sizes are around 100 picometers (a ten-billionth of a meter, in the short scale)
6-Protons and neutrons are called nucleons.
7-The protons have a positive electric charge, the electrons have a negative electric charge, and the neutrons have no electric charge.
8-Atoms can attach to one or more other atoms by chemical bonds to form chemical compounds such as molecules.
9- The number of neutrons defines the isotope of the element. The number of electrons influences the magnetic properties of an atom.
10-In the early 1800s, John Dalton used the concept of atoms to explain why elements always react in ratios of small whole numbers (the law of multiple proportions).
11-In 1827, botanist Robert Brown used a microscope to look at dust grains floating in water and discovered that they moved about erratically, a phenomenon that became known as “Brownian motion”.
12-French physicist Jean Perrin used Einstein’s work to experimentally determine the mass and dimensions of atoms, thereby conclusively verifying Dalton’s atomic theory.
13-The term isotope was coined by Margaret Todd as a suitable name for different atoms that belong to the same element.
14-J.J. Thomson created a technique for separating atom types through his work on ionized gases, which subsequently led to the discovery of stable isotopes.
15-In 1913 the physicist Niels Bohr proposed a model in which the electrons of an atom were assumed to orbit the nucleus but could only do so in a finite set of orbits, and could jump between these orbits only in discrete changes of energy corresponding to absorption or radiation of a photon.
16- In 1944, Hahn received the Nobel prize in chemistry.
17-The neutron was discovered in 1932 by the English physicist James Chadwick.
18-The proton, the electron, and the neutron are classified as fermions.
19-Valency is the combining power of an element. It is equal to number of hydrogen atoms that atom can combine or displace in forming compounds
20-The outermost electron shell of an atom in its uncombined state is known as the valence shell, and the electrons in that shell are called valence electrons.
21-The Earth contains approximately 1.33×1050 atoms.
1-Created by Dmitri Mendeleev (1834-1907), the periodic table orders all known elements in accordance to their similarities
2-The periodic table is a chart that categorizes elements by “groups” and “periods.” All elements are ordered by their atomic number.
3-The atomic number is the number of protons per atom. In a neutral atom, the number of electrons equals the number of protons. The periodic table represents neutral atoms.
4-. Atomic mass is measured in Atomic Mass Units where 1 amu = (1/12) mass of carbon measured in grams.
5- The atomic mass number is equal to the number of protons plus neutrons, which provides the average weight of all isotopes of any given element.
6-Atoms with the same atomic number, but different mass numbers are called isotopes.
7-An atom is the smallest building block of matter. Atoms are made of neutrons, protons and electrons.
8-There are two main classifications in the periodic table, ‘groups’ and ‘periods’.
9-Groups are the vertical columns that include elements with similar chemical and physical properties. Periods are the horizontal rows.
10-An electron has a negative charge, a proton has a positive charge and a neutron has no charge.
11-There are different models of the structure of the atom. One of the first models was created by Niels Bohr, a Danish physicist. He proposed a model in which electrons circle the nucleus in “orbits” around the nucleus, much in the same way as planets orbit the sun
Periodic Table -Important Points
1- Going from left to right on the periodic table, you will find metals, then metalloids, and finally nonmetals.
2-The 4th, 5th, and 6th periods are called the transition metals. These elements are all metals and can be found pure in nature.
3- The transition metals include two periods known as the lanthanides and the actinides, which are located at the very bottom of the periodic table.
