Chemical Elements

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What is a Chemical Element?

Answer:A chemical element, or an element, is a material which cannot be

broken down or changed into another substance using chemical means. Elements may be thought of as the basic chemical building blocks of matter. Depending on how much evidence you require to prove a new element has been created, there are 117 or 118 known elements.

All substances consist of matter. Matter is anything which has mass and takes up space. Some important concepts to remember about matter are:

• Matter is made up of one or more of over 92 naturally-occurring elements.

• Each element is a pure substance, made up of only one type of atom.

Hydrogen Atom

The Periodic Table The periodic table is a chart which organizes the chemical elements.

The elements are categorized according to the following attributes:• Atomic Number - number of protons in the nucleus• Atomic Mass - sum of the number of protons plus neutrons in the

nucleus• Atomic weight - total mass of protons, neutrons and electrons.The unit of mass for atoms and their particles is the DALTON. A neutron

has a mass of 1.008 daltons; a proton 1.007 daltons; an electron 0.0005 daltons, hence practically all the mass of an atom is in the nucleus.

Group - columns or multiple columns in the periodic table: -elements in a group share similar chemical and physical properties.Period - rows from left to right in the period table: -elements in a period have the same number of energy shells.

The Periodic Table

Atom and Its Structure

• Chemistry is the study of matter and the interactions between different types of matter and energy. The fundamental building block of matter is the atom. An atom consists of three main parts: protons, neutrons, and electrons. Protons have a positive electrical charge. Neutrons have no electrical charge. Electrons have a negative electrical charge. Protons and neutrons are found together in what is called the nucleus of the atom. Electrons circle around nucleus.

Oxygen

Carbon (1)

Carbon (2)

Aluminium

Silver

Isotopes

The difference between one element and other is due to the difference in the number of protons in their atoms. However, some atoms of the same element have different numbers of neutrons. These different atoms are called isotopes of the element. All isotopes have the same chemical properties because the chemical properties of an element are determined by their electrons and all atoms of an element have the same number of electrons.

Electrons

• Electrons posses different amounts of energy and are located in numbered energy levels up to n = 7. Electron levels are sometimes called energy shells and are labelled: K, L, M, N, etc. To achieve stability, atoms either empty their outermost energy levels or fill it up to the maximum. In so doing they may give up, accept or share electrons with other atoms, whichever is easiest. The VALENCE (combining capacity) is the number of of extra or deficient electrons in the valence energy level.

BONDS

• ANIMAL BONDING• HUMAN BONDING• CHEMICAL BONDS

ANIMAL BONDING 1

ANIMAL BONDING 2

ANIMAL BONDING 3

ANIMAL BONDING 4

ANIMAL BONDING 5

ANIMAL BONDING 6

HUMAN BONDING 1

HUMAN BONDING 2

HUMAN BONDING 3

HUMAN BONDING 4

HUMAN BONDING 4

HUMAN BONDING 5

Chemical Compounds - Chemical Bonds

A compound is a combination of two or more chemically-bonded elements.

• IONIC BONDS• COVALENT BONDS• HYDROGEN BONDS

Ionic Bonds

In ionic bonds, electrons are actually transferred from one atom to another. Such attoms or aggregates of atoms are then called ions. The atom gaining an electron or electrons becomes negatively charged, called an anion. The atom which loses electrons becomes positively charged, called a cation. Since oppositely charged partticles attract each other, oppositely charged ions can be held together by this attraction to form electrically neutral ionic compounds. Such attracttions are called IONIC BONDS.

Covalent Bonds

In covalent bonds, atoms share electrons in their outer energy level. If one pair of electrons are shared (e.g. H2) a SINGLE covalent bond is formed. Two pairs shared (e.g O2) form a DOUBLE bond. Three pairs (e.g. N2) a TRIPLE bond. Shared electrons, attracted equally to both atoms, as with H2, form a NON-POLAR COVALENT BOND. However, if one atom attracts the shared electrons more strongly than the other, the bond is a POLAR COVALENT BOND and produces polar molecules with positive and negative areas. Water is a polar molecule.

Ionic & Covalent Bonding

Hydrogen Bonds

Oppositely charged regions of polar molecules can attract one another. Such a bond between hydrogen and e.g. Oxygen or nitrogen is called a HYDROGEN BOND. These occur in water, proteins and other large molecules but are weak bonds (5% as strong as covalent bonds). However, large molecules may contain many H-bonds, e.g. between bases in DNA and can thus give strength and three-dimensional shape to, e.g proteins and nucleic acids.

Hydrogen Bonding

Basic Constituents of ProtoplasmELEMENTS PERCENTAGE MAKE (H+O) MAKE (H+0+C) MAKE (H+O+C+N)

H - HYDROGEN 9.5% WATER CARBOHYDRATES & LIPIDS

PROTEINS

O - OXYGEN 65.0%

C - CARBON 18.5%

N - NITROGEN 3.2%

Mixtures

A mixture is defined as an impure substance made up of two or more types of elements (atoms) or compounds or both mechanically mixed in any proportion, and it can be further subdivided into simpler substances by physical (mechanical) means.

• The constituents of a mixture retain their original properties. • The constituents of a homogenous mixture are uniformly mixed

thoroughout the mixture. The properties and composition of a homogenous mixture are the same throughout the mixture.

• The constituents of a heterogenous mixture are not uniformly mixed thoroughout the mixture. The properties and composition of a heterogenous mixture are not the same throughout the mixture.

Mixtures

Examples of Mixtures • Stainless steel is a mixture (alloy) of iron,

carbon, chromium, and nickel. Carbon gives hardness to the mixture. Chromium and nickel give a silvery look to the mixture.

• Potassium sulfide solution is a homogenous mixture.

• A mixture of water and oil is heterogenous in nature.

Compounds

A compound is defined as a pure substance made up of two or more types of elements (atoms) chemically combined in a fixed proportion, and it can be further subdivided into simpler substances by chemical means only.

• A molecule is the smallest part of a compound, whose properties are the same as those of the compound.

• A compound can be represented by using a chemical formula. • Examples of Compounds • The chemical formulae H2O and FeS represent the

compounds water and Ferrous sulfide (Iron [I] sulfide) respectively.

States of Matter

• There are five main states of matter. Solids, liquids, gases, plasmas, and Bose-Einstein condensates are all different states of matter. Each of these states is also known as a phase. Elements and compounds can move from one phase to another phase when special physical forces are present. One example of those forces is temperature. The phase or state of matter can change when the temperature changes. Generally, as the temperature rises, matter moves to a more active state.