Notes, abstracts, papers, exams and problems of Chemistry

Q#6.3: Define (i) Crystal lattice (ii) Unit Cell.

Ans.(i) Crystal Lattice.

A particular three-dimensional arrangement of particles (atoms, ions, molecules) in a crystal is called a crystal lattice.

In a crystal lattice, particles are located at definite positions in space. These positions are represented by points in a crystal and are called lattice points or lattice sites. This arrangement is called a crystal lattice or space lattice. A crystal lattice actually shows the shape of a crystal.

(ii) Unit Cell.

The smallest geometrical portion of the crystal which is used to build up the whole crystal. OR

If is the smallest portion of a crystal lattice which includes all the positions of each type of particle in the crystal. For example, a cubic crystal... Continue reading "Crystal Lattice and Unit Cell" »

An ion is an atom which has more or less electrons than protons

Hazard Symbols

Hazard symbols explain why a substance must be handled carefully.

Air Pollution from Burning Fossil Fuels

Complete combustion - the fuel reacts completely with oxygen, e.g.:

hydrocarbon + oxygen → carbon dioxide + water

Incomplete combustion - the fuel only partly reacts with oxygen, e.g.:

hydrocarbon + oxygen → carbon dioxide + water + carbon monoxide + carbon (soot)

Impurities in fossil fuels, such as sulfur, also react with oxygen when heated:

sulfur + oxygen → sulfur dioxide

At the very high temperatures in vehicle engines, nitrogen gas from the air reacts with oxygen:

nitrogen + oxygen → nitrogen oxides

Many products from burning fossil fuels are pollutants; they harm habitats and their organisms.

Acid Rain

Acid rain is rainwater... Continue reading "Combustion, Oxidation, and Environmental Impact" »

C

Circumnavigate

To sail or travel all the way around.

Citadel

A fortress defending a city.

Clandestine

Concealed or secret for an evil purpose.

Classic

Of the highest quality.

Cleave

To cling.

Climatic

Having to do with the climate.

Cloister

Covered walk, with columns on one side.

Clone

An exact duplicate.

Clout

A blow.

Cloy

To cause to feel too full when eating; overly sweet.

Coddle

To baby.

Cogitate

To ponder.

Cohort

A group.

Commemorate

To honor the memory of.

Commiserate

To express sorrow or sympathy for.

Commodious

Spacious, roomy.

Compatible

Harmonious.

Competent

Capable.

Compile

To gather together.

Comply

To act or be in accordance with.

Composed

Calm.

Compromise

A settlement of differences in which each side gives up something.

Compunction

Remorse.

Concave

Curved inward.

Concede

To

Chemical Change vs. Phase Change

Chemical change: Produces new substances that didn't exist before.

Phase change: The substance remains the same before and after the process.

Dissolving: It is only a homogeneous mixture; no new substances appear.

Identifying Chemical Changes

How do we know if a chemical change is occurring?

• Gas release: Gases may not be visible; we identify them by bubbles in a liquid.
• Color change
• Thermal energy change
• Energy release as light

Understanding Chemical Reactions

A chemical reaction occurs when the starting substances, called reactants, transform into other new substances, called products.

The appearance of new substances is due to the rearrangement of the reactant's atoms, forming the products. The information about a chemical... Continue reading "Chemical Reactions and Their Impact on Industry" »

Ozone (O3 ) is a made with three oxygen atoms; it is very unstable and has a short lifetime. At room Temperature and pressure has acrid odour and no colour, although at high concentration levels can turn Into blue. At high concentrations can be toxic and can cause death. It s not emitted directly into the air, but is created by chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOC) in the presence of sunlight. VOC + NOx + sunlight tropospheric O3Particulate Matter (PM) "Particulate matter," also known as particle pollution or PM, is a complex mixture of extremely small Particles and liquid droplets. Particle pollution is made up of a number of components, including acids (such as nitrates and sulfates), organic... Continue reading "Divergence in the upper air results, near the surface in: atpl" »

1. Structure of an atom -  An atom is composed of protons, electrons, and neutrons. The entire mass of an atom is concentrated in the nucleus which is at the centre.

   1. Protons - Protons are the positively charged particles which are present in the nucleus of an atom.

   2. Neutrons - Neutrons are the particles in an atom that have a neutral charge. 

   3. Electrons - An electron is a negatively charged subatomic particle that can be either bound to an atom or free

   4. Atomic Mass (what it represents) - The atomic number refers to the number of protons in the atom's nucleus, 

   5. Atomic Number (what it represents) - The atomic mass of an element represent the average total mass of its neutrons, protons, and electrons

2. Standard Atomic Notation

   1. How to determine how many neutrons,

Three major characteristics of life

The cell theory

Three major domains of life

Ductility: Able to undergo change of form without breaking

·Malleability: capable of being shaped, as by Hammering or pressing:

·Density (give an Example): a measurement of how Tightly matter is crammed together. Example: Oil floats on vinegar because Its density is less.

• Chemical properties of matter (give an Example): Are any of the properties Of matter that may only be observed and measured by performing a chemical change or chemical Reaction. Example: oxidation states

·What is a physical Change (give an example): A usually reversible change in the physical 

properties of a substance,as size or shape. Example: When melting an ice cube.

·Difference between Chemical properties and physical properties (give an example)