Melting and Boiling

                                Melting and Boiling

As we learned in solids, liquids, and gases all matter exists in certain states or phases. Water can be liquid water, solid ice, or gas vapor. It's still all water, however, and made up of molecules of 2 hydrogen atoms and 1 oxygen atom (H2O). 

 
Lava is melted or liquid rock

Melting and Freezing 

When a solid turns into a liquid it is called melting. There is a temperature at which this happens called the melting point. As the energy in the molecules increases from a rise in temperature, the molecules start moving faster. Soon they have enough energy to break free of their rigid structure and start moving around more easily. The matter becomes a liquid. The melting point for water is 0 degrees C (32 degrees F). 

When the opposite happens and a liquid turns into a solid, it is called freezing. 

Boiling and Condensation 

When a liquid becomes a gas it is called boiling or vaporization. Again, at a certain temperature called the boiling point, the molecules will gain enough energy to break free and become a gas. The boiling point for water is 100 degrees C (212 degrees F).

 
Hot gas from steam engine condensing

When the opposite occurs and a gas becomes a liquid, it is called condensation. 

Evaporation 

Evaporation is liquid becoming a gas that happens only on the surface of a liquid. Evaporation doesn't always need a high temperature to occur. Even though the overall energy and temperature of a liquid may be low, the molecules on the surface that are in contact with the air and gases around them, can be high energy. These molecules on the surface will slowly become gases through evaporation. You can see evaporation when water on your skin dries or a puddle in the street slowly goes away. 

Standard State 

Scientist use the term "standard state" to describe the state an element or substance is in at "room conditions" of 25 degrees C and one atmosphere of air pressure. Most of the elements, like gold and iron, are solids in their standard state. Only two elements are liquid in their standard states: mercury and bromine. Some of the elements that are gases in their natural state include hydrogen, oxygen, nitrogen, and the noble gases. 

Fun facts about Melting and Boiling

• When rocks get really hot they turn into a liquid called magma or lava.
• Gas can be turned into a liquid through pressure. By squeezing all the gas molecules tightly together a gas can become liquid.
• We use natural gas in our homes in its gas state, but when it's shipped in ocean tankers it's shipped in a liquid state to save on space.
• Mercury has the interesting properties of being both a metal and a liquid in its standard state.

Pure Substances and Mixtures

                     Pure Substances and Mixtures

What is matter?

Matter can be defined as any substance that has inertia, occupies space and has mass.

How is matter classified?

Scientists of the world classify matter as solid, liquid or gas, but there is one more interesting way to classify it. Matter can also be classified as pure substances and mixtures.

What is a pure substance?

A pure substance is a type of matter which exists in its most basic or purest form and cannot be broken down further. Examples of pure substances include water, gases like carbon dioxide, oxygen and metals like platinum, gold and silver.

Each pure substance has its own set of unique chemical and physical properties which helps us in identifying it.

Examples of pure substances

Water has a freezing and melting point of 0°C and a boiling point of 100°C. It is colourless, tasteless and odourless.
Gold is considered pure at 24 karat. It is yellow in color, solid at room temperature and is regarded as a good conductor of electricity. It is also malleable and ductile in nature.

Types of pure substances

Pure substances can be divided into two categories – elements and compounds.
Elements are made up of the same types of atoms. The known elements listed in the periodic table can be considered pure substances. Examples of elements include hydrogen, oxygen, gold, silver
Compounds are made up of different types of atoms joined together by chemical bonds. Examples of compounds include water, glucose, salt and carbon dioxide.

What is a mixture?

Mixture is a combination of two or more pure substances where each substance keeps its own identity upon mixing. Mixtures are present almost everywhere on Earth. Look at rocks, the ocean, rivers or even the atmosphere. All of them are mixtures! In other words, anything that you can mix together is a mixture. Even the foods you eat.

Why is it called a mixture?

It means the fundamental chemical structure of the components in a mixture does not change upon mixing.

Examples of mixtures

Although water is a pure substance, if you put sand into a glass of water, it would turn into a mixture. Each of the components of a mixture can be separated from one another. You can always separate the sand from water by filtering it.

If you take a mixture of salt and water, you can separate it by evaporating the water, to get salt in the container. Air, too, is a mixture of different gases such as carbon dioxide, oxygen, nitrogen and water vapour etc. Blood is a mixture made up of different types of blood cells and plasma.

Types of mixtures

1. Homogeneous mixture – The components of a homogeneous mixture have a uniform composition, and cannot be seen separately. The prefix ‘homo’ means same and it tells us that when two substances combine extremely well with one another, they form a uniform mixture. For example, sugar and water do not chemically react and form another compound although the water does turn sweet!
2. Heterogeneous mixture – The components of a heterogeneous mixture do not have a uniform composition and can be viewed separately without losing their identity. For example, if you mix sulfur powder with iron dust, you can easily see the two separately. You can even separate the iron dust by using a magnet.

How do we differentiate between pure substances and mixtures?

• A Pure Substance is matter which cannot be separated into its basic components by using a physical or a chemical process. The physical and chemical properties of pure substances are non-changing, if it is on its own without disturbing.
• A Mixture is made up of a combination of two or more substances that are not united using a chemical reaction. The physical and chemical properties of mixtures vary.

What is an Atom and a Molecule

What is an Atom and a Molecule 

Periodic Table and the Elements

Periodic Table and the Elements

Now we're getting to the heart and soul of the way the Universe works. You know that a generic atom has some protons and neutronsin the nucleus and some electrons zipping around in orbitals. When those pieces start combining in specific numbers, you can build atoms with recognizable traits. If you have eight protons, neutrons and electrons, you will have an oxygen (O) atom. If you have seven protons, neutrons, and electrons, you will have a nitrogen (N) atom. The atoms for each element are unique, even though they are all made of similar subatomic parts. 

Remember that 'atom' is the general term. Everything is made of atoms. The term 'element' is used to describe atoms with specific characteristics. There are almost 120 known elements. For example, you are made up of billions of billions of atoms but you probably won't find more than 40 elements (types of atoms) in your body. Chemists have learned that over 95% of your body is made up of hydrogen (H), carbon (C), nitrogen, oxygen, phosphorus (P), and calcium (Ca). 

The Same Everywhere

As far as we know, there are a limited number of basic elements. Up to this point in time, we have discovered or created about 120. Scientists just confirmed the creation of element 117 in 2014. While there are more elements to discover, the basic elements remain the same. Iron (Fe) atoms found on Earth are identical to iron atoms found on meteorites. The iron atoms in the red soil of Mars are also the same. 

With the tools you learn here, you can explore and understand the Universe. You will never stop discovering new reactions and compounds, but the elements will be the same. 

The List of Elements

Since the launch of the site, we've been asked, "Why start with 18?" The rules for the first eighteen elements are very straightforward: 

(1) Electrons fit nicely into three orbitals. Remember that the orbitals are the places you will generally find the electrons as they spin around the nucleus. 
(2) These eighteen elements make up most of the matter in the Universe.
(3) It's a lot easier to remember facts about 18 elements than over 100 elements. 

Element 1: Hydrogen Element 2: Helium Element 3: Lithium Element 4: Beryllium Element 5: Boron Element 6: Carbon Element 7: Nitrogen Element 8: Oxygen Element 9: Fluorine

Element 10: Neon Element 11: Sodium Element 12: Magnesium Element 13: Aluminum Element 14: Silicon Element 15: Phosphorus Element 16: Sulfur Element 17: Chlorine Element 18: Argon

As we move past the first eighteen elements, you can start to learn about transition elements in the fourth period (row) of the periodic table. The transition metals have electron configurations that are a little different from the first eighteen. Make sure you understand the basics of electron orbitals before you move on to this row. 

Element 19: Potassium Element 20: Calcium Element 21: Scandium Element 22: Titanium Element 23: Vanadium Element 24: Chromium Element 25: Manganese Element 26: Iron Element 27: Cobalt

Element 28: Nickel Element 29: Copper Element 30: Zinc Element 31: Gallium Element 32: Germanium Element 33: Arsenic Element 34: Selenium Element 35: Bromine Element 36: Krypton

Structure of An Atom

Structure of An Atom

What is an atom?

Everything in our universe is made of matter and matter is made of atoms. An atom maybe described as the smallest particle that matter is made with and has the properties of a chemical element. An atom is minute in size and typical sizes are in picometers, a ten billionth of a meter.

What are atoms made of?

An atom is made of three parts – protons, neutrons and electrons.

Each of these parts has an associated charge. The protons carry a positive charge, electrons have a negative charge and neutron possess no charge. Protons and neutrons make up the nucleus of the atom and electrons orbit the nucleus at different energy levels.

What is atomic number?

Atomic number of an atom is defined by the number of protons in the nucleus of an atom.

What is atomic mass?

Atomic mass of an atom is equivalent to the number of protons and neutrons in the atom.

Parts of an atom

What is a proton?

A proton is a positively charged particle found within the atom’s nucleus. Rutherford discovered them in his experiments with cathode ray tubes.

The number of protons in an atom define what the element is. This is what is referred to as the atomic number of that element. The number of protons also determine the chemical behaviour of that element.

What is a neutron?

A neutron is the neutral part of the atom’s nucleus, with no electric charge, and a mass slightly larger than that of a proton. It was discovered by the English physicist, James Chadwick.
Neutrons and protons combined make up the mass of the atom. We can find the number of neutrons if we know the atomic mass and the atomic number of an element, using this simple equation.

Atomic Mass – Atomic Number = Number of Neutrons

Atoms of the same element may have different number of neutrons. Adding neutrons changes the radioactivity of the element, without changing the charge of the atom. This is important in nuclear physics.

What is an electron?

An electron is a negatively charged part of the atom found outside the nucleus in orbits and are attached to the protons in the atom with electromagnetic force. Closer the electron to the nucleus, the stronger the electromagnetic force between them.

Electrons can escape from their orbit in response to an external energy being applied. It can also change its state to a higher energy level by absorbing a photon with sufficient energy to boost it to a new quantum state. It can also drop down to lower energy state emitting the excessive energy as a photon.

Atoms are neutral if the number of protons and electrons are equal. Atoms that have an excess or deficit of electrons are called ions. Electrons have no internal structure, though protons and neutrons on the other hand are made of quarks.

Thomson’s model of an atom

The Thomson Model of an atom was proposed by JJ Thomson, in 1897. He discovered electrons while experimenting with cathode ray tube. The cathode ray tube was negatively charged. He also studied positively charged particles in neon gas. Although his theory explained somethings about atoms and electrons, it failed to provide sufficient information about the positively charged particles and the nucleus of the atom.

Rutherford model of an atom

After the model of an atom, by Thomson, was unable to explain the positively charged particles in an atom, Ernest Rutherford proved the presence of positively charged particles in the nucleus of an atom through the gold foil experiment. This theory proved that the nucleus of an atom contains positively charged particles.

Bohr’s model of an atom

Bohr’s model of an atom was proposed by Neil Bohr in 1915. He specified that electrons move in fixed orbits/shells, which have fixed energy levels.

What is valency?

Valency is a measure of the reactivity of an atom. It is defined by the capacity of the atom to lose or gain valence electrons in the valence shell.
Every atom wants to have 8 electrons in the valence shell and this is known as the octet rule.

What are isotopes?

Isotopes are atoms with the same number of protons but that have a different number of neutrons. Since the atomic number is equal to the number of protons and neutrons, isotopes have the same atomic number, but different mass numbers.

Carbon 14, used in carbon dating to find out the age of really old archeological and biological remains, is an isotope of carbon.

Tritium, an isotope of hydrogen, is used to make glow in the dark faces on clocks and wrist watches.

What Is Chemistry?

Modal verbs and their meaning

What are modal verbs?

Modals (also called modal verbs, modal auxiliary verbs, modal auxiliaries) are special verbs which behave irregularly in English. They are different from normal verbs like "work, play, visit..." They give additional information about the function of the main verb that follows it. They have a great variety of communicative functions.
Here are some characteristics of modal verbs:

• They never change their form. You can't add "s", "ed", "ing"...
• They are always followed by an infinitive without "to" (e.i. the bare infinitive.)
• They are used to indicate modality allow speakers to express certainty, possibility, willingness, obligation, necessity, ability

List of modal verbs

Here is a list of modal verbs:

can, could, may, might, will, would, shall, should, must

The verbs or expressions dare, ought to, had better, and need not behave like modal auxiliaries to a large extent and my be added to the above list

Use of modal verbs:

Modal verbs are used to express functions such as:

1. Permission
2. Ability
3. Obligation
4. Prohibition
5. Lack of necessity
6. Advice
7. possibility
8. probability

Examples of modal verbs

Here is a list of modals with examples:

Modal Verb	Expressing	Example
must	Strong obligation	You must stop when the traffic lights turn red.
	logical conclusion / Certainty	He must be very tired. He's been working all day long.
must not	prohibition	You must not smoke in the hospital.
can	ability	I can swim.
	permission	Can I use your phone please?
	possibility	Smoking can cause cancer.
could	ability in the past	When I was younger I could run fast.
	polite permission	Excuse me, could I just say something?
	possibility	It could rain tomorrow!
may	permission	May I use your phone please?
	possibility, probability	It may rain tomorrow!
might	polite permission	Might I suggest an idea?
	possibility, probability	I might go on holiday to Australia next year.
need not	lack of necessity/absence of obligation	I need not buy tomatoes. There are plenty of tomatoes in the fridge.
should/ought to	50 % obligation	I should / ought to see a doctor. I have a terrible headache.
	advice	You should / ought to revise your lessons
	logical conclusion	He should / ought to be very tired. He's been working all day long.
had better	advice	You 'd better revise your lessons

Remember

Modal verbs are followed by an infinitive without "to", also called the bare infinitive.

Examples:

• You must stop when the traffic lights turn red.
• You should see to the doctor.
• There are a lot of tomatoes in the fridge. You need not buy any