• The ancient philosophers believed that matter was composed of four fundamental substances—earth, air, fire, and water.

• Now,it is established that matter is much more complex, and is made up of 91 naturally occurring fundamental substances, or elements, in millions of unique combinations.

• Chemistry is the study of matter—its nature, properties, and transformations

• Matter is anything physically real i.e. anything with mass and volume.

• Any characteristic used to describe or identify something is called a property.

  1. chemical composition - describes what matter is made of.

  2. chemical reactivity - which describes how matter behaves.

• Physical changes alter with the outer condition/state of a substance whereas Chemical changes alter the chemical make up of the substance.

Matter exists in three forms-Solid, Liquid and Gas.

• Pure substance is uniform in its chemical composition and its properties all the way down to the microscopic level.

• Mixtures are of two types- Homogenous mixture and Heterogenous mixtures.

  • Homogenous mixture:

    • blend of two or more pure substances having a uniform composition at the microscopic level.

    • Mixture components can be separated out without any change in properties.

    • eg: sugar dissolved in water.

  • HETEROGENOUS MIXTURE:

    • Blend of two or more substances having non uniform composition.

    • Mixture components may have a change in properties after getting separated out.

    • eg: vegetable stew in which each spoonful is different,

• A pure substance that cannot be broken down chemically into simpler substances is called an element.

• Any pure material that can be broken down into simpler substances by a chemical change is called a chemical compound. The term compound implies “more than one”.

• 118 elements have been found until now.

  • 91 elements occur naturally; the remaining elements have been produced artificially by chemists and physicists.

  • Each element has its own distinctive properties, and just about all of the first 95 elements have been put to use in some way that takes advantage of those properties.

• Oxygen and silicon together account for nearly 75% of the mass in the earth’s crust; oxygen, carbon, and hydrogen account for nearly all the mass of a human body.

• symbols are combined to produce chemical formulas, which use subscripts to identify how many atoms of each element are in a given chemical compound.

• Chemical reactions represent chemical changes using symbolic shorthand notations. They consist of reactants and products.

• Mass, volume, temperature, density, and other physical properties that can be measured are called physical quantities and are described by both a number and a unit that defines the nature and magnitude of the number.

• Materials can be measured with several different units of measurement and thus to avoid confusion, we have a standard unit system called SI units.

• Rather than write very large or very small numbers in their entirety, it is more convenient to express them using scientific notations.

• A number is written in scientific notation as the product of a number between 1 and 10, times the number 10 raised to a power.

• Mass is a measure of the amount of matter in an object, whereas weight is a measure of the gravitational pull that the earth, moon, or other large body exerts on an object.

• The mass of an object can be determined by comparing the weight of the object to the weight of a known reference standard.

• The mass of an object provides us with important information about its composition, i.e what elements it contains. But mass is not the only property that can be used to distinguish between objects.

• The total number of digits used to express such a measurement is called the number of significant figures.

• The following rules are helpful for determining the number of significant figures when zeroes are present:

  • RULE 1:Zeroes in the middle of a number are like any other digit; they are always significant.

  • RULE 2:Zeroes at the beginning of a number are not significant; they act only to locate the decimal point.

  • RULE 3:Zeroes at the end of a number and after the decimal point are significant.

  • RULE 4:Zeroes at the end of a number and before an implied decimal point may or may not be significant.

• The simplest way to carry out calculations involving different units is to use the factor-label method.

FACTOR LABEL METHOD → a quantity in one unit is converted into an equivalent quantity in a different unit by using a conversion factor that expresses the relationship between units: Starting quantity * Conversion factor = Equivalent quantity.

• All chemical reactions are accompanied by a change in energy, which is defined in scientific terms as the capacity to do work or supply heat.

• Temperature, the measure of the amount of heat energy in an object, is commonly reported either in Fahrenheit (°F) or Celsius (°C) units. The SI unit for reporting temperature, however, is the kelvin (K).

  • Temperature in K = Temperature in °C + 273.15

  • Temperature in °C = Temperature in K - 273.15

• Celsius to Fahrenheit: °F = ( (1.8°F/ °C) * °C) + 32 °F

• Fahrenheit to Celsius: °C = ( °C /1.8 °F) b *( °F - 32 °F)

• The amount of heat needed to raise the temperature of 1 g of a substance by 1 °C is called the specific heat of the substance. It is measured in units of cal.

• Density of a substance is mass of the substance divided by the volume of the substance.

• The specific gravity of a substance (usually a liquid) is simply the density of the substance divided by the density of water at the same temperature. It is unitless.