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Learn about the basics of chemistry, including the concept of matter, atoms, elements, isotopes, the periodic table, metals, nonmetals, metalloids, compounds, molecules, and ions.
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WELCOMETO AP CHEMISTRY MAHUA CHAKRABORTY
What is Matter • Matter is anything that has mass and takes up space. • Examples are rockets, paper, notebook, a car.
Atoms and Elements • Smallest particle of any element is called an atom. • An element is a substance composed of only one kind of atom. Each element is represented by a chemical symbol made up of one or two letters. • Example for one letter elements are Hydrogen H, Nitrogen N .. • Example for two letter elements are Magnesium Mg, Calcium Ca, Silicon Si.
The Nuclear Atom • Atoms are made up of subatomic particles called electrons, protons, and neutrons. • Protons and Neutrons form a compact, central body which is the nucleus of the atom. • Electrons are like a cloud around the nucleus. • Protons are positively charged and electrons are negatively charged. • Neutrons however don’t have any charge.
The number of protons in an atomic nucleus is called the atomic number. • It is denoted by Z. • There is an equal number of electrons surrounding the nucleus. • The atom has no charge. • The total number of protons and neutrons is called the mass number . • This is denoted by A. • Neutrons and protons jointly are called nucleons.
Isotopes • Atoms with same atomic number but with different mass numbers are called isotopes. • An isotope is named by writing its mass number after the name of the element, as in neon-20,neon-21,and neon 22. • Symbol is written by adding the mass number as a superscript to the left of the chemical symbol of the element e.g.20Ne,21Ne,and 22Ne.
Properties Of Isotopes • Isotopes of the same element have the same number of protons and the same number of electrons they have essentially the same properties. • An exception of this is hydrogen. The mass differences between isotopes are relatively large. As a result hydrogen isotopes have differences in the properties. • Examples of isotopes of hydrogen are Deuterium(2H) and Tritium(3H).
Class Practice • How many protons, neutrons and electrons are present in a) an atom of nitrogen-15 b) an atom of iron-56. • Write the symbols of the isotopes of a) argon b) calcium that have the same number of neutrons as 40K.
The Periodic table • The periodic table is made up of vertical columns called groups and horizontal rows called periods. • The members of each group show similarity with one another. • The 1st group is the alkali metals. • The 2nd group is the alkaline earth metals. • Groups 3-11 contain the transition metals. • Groups 12,13 and 14 are the having less active metals. E.g. Pb and In. • Group 17 constitutes the halogen group. • Group 18 constitutes the noble gas.
The long block shown below the main table is the inner transition metals. • Elements in the upper row begins with lanthanum so it is called the lanthanides. • Elements in the lower row begins with actinium hence it is called as actinides.
Metals, Nonmetals and Metalloids • Metals conduct electricity, has a metallic luster and is malleable and ductile e.g. Na, Cu, and Au. • Nonmetals do not conduct electricity and is neither malleable nor ductile e.g. S, C, and P.. • Metalloids has the appearance and some physical properties of a metal but behaves chemically like a nonmetal e.g. Ge, Si..
What are Compounds • Compound is a substance that consists of two or more different elements with their atoms in a definite, characteristic ratio. • Two types of compounds Organic and inorganic compounds. • Organic compounds are compounds containing Carbon and Hydrogen. • Inorganic compounds include water, ammonia, hydrochloric acid etc.
Molecules • Molecule is a definite electrically neutral group of atoms bonded together e.g. H2O. • All gaseous elements are found as diatomic molecules. e.g. O2 , Cl2.
Formulas • Chemical Formula tells us which element is present and the subscript tells us how many atoms of that element is present. e.g. O2 ,S8 and P4. • Structural Formula represents the atoms by their elemental symbols and use lines to show which atoms are joined together. • E.g.
Models • Ball and Stick Model • The colored balls depict the atoms and the sticks indicate the links between them.
Tube Structure • This structure omits the balls and represents the atoms and the links between them by colored lengths of tube.
Ions and Ionic Compounds • Ionic compounds consists of positive and negative ions held together by the attraction between their opposite charges. E.g. Sodium chloride consists of alternate Na+ and Cl – ions. • Positively charged ions are called cations and negatively charged ions are anions. • Na+ means sodium atom that has lost one electron and hence has a single positive charge. • Cl- means chlorine has gained an electron that increases the negative charge by one atom.
Chemical Formulas Of Ionic Compounds • Ionic compounds does not consist of individual molecules. • Ratio of the number of cations to the number of anions is the same for any sample of a given compound we can use that ratio to write its formula. • In sodium chloride there is one Na+ cations for each Cl- ion, so its formula is NaCl.
Examples of poly atomic cations ammonium ion NH4+. • Polyatomic anions are called oxo anions e.g. CO32- • Formula unit is a group of ions with a composition given by the formula of an ionic compound. • Formula unit for NaCl consists of one Na+ and one Cl- ion. For ammonium sulfate consists of two NH4+ ions and one SO42-ion.
Class Practice • Identify the type of each substance and give the number of atoms of each element in the formula units or molecules of the compounds a)N2O4 b)(NH4)3PO4 c)P4
Mixtures • Elements and Compounds are pure substance. • Mixtures are simple substance which are neither element nor compounds. • Gasoline is a mixture of hydrocarbons and additives blended together to achieve efficient combustion. • Alloys are mixtures of metals formulated for maximum strength and resistance to corrosion.
Mixtures Compounds can be separated by using physical techniques. Composition is variable. Properties are related to those of its components Compounds Components cannot be separated by using physical techniques. Composition is fixed. Properties are unlike those of its components Mixture And Compounds
Heterogeneous In this type we can identify the different components of the mixture. Examples are sand and sugar Milk if seen through microscope you can see individual globules of butterfat. Homogenous In this type the individual components cannot be separated Example syrup of sugar and water. White vinegar. Types Of Mixtures
Separation techniques • To analyze the composition of a sample that we suspect is a mixture we need to separate its components. • Filtration: Makes use of differences in solubility. The sample is shaken with a liquid and then poured through a mesh, the filter. You can separate the soluble material that passes through the filter and the insoluble is captured by the filter.
Distillation: This technique makes use of the difference in the boiling points. Can be used to separate two liquids having different boiling point or a mixture of a salt and water where the boiling point of the salt is much higher than the boiling point of water.
Chromatography: This technique depends on the different abilities of substances to adsorb or stick to surfaces. The mixture is washed across a strip of filter paper. Substances that adsorb weakly move far apart than others. Colored components give rise to separate patches of color on the paper.
Molecular Compounds • Binary molecular compounds are built from 2 elements. • Example Phosphorus trichloride PCl3 and carbon monoxide CO. • The oxo acids are molecular compounds that are the parents of oxo anions e.g. sulfuric acid is the molecular compound.SO42- has 2 negative charges. To balance this two H+ ions are needed.
Class Practice • Give the systematic names of the compounds a)N2O4 b)ClO4
