The textbook answers are given as ~ “molecule is the smallest particle of a pure chemical substance that still retains its composition and chemical properties".
Though the textbook definition of the word molecule can sometimes be a bit complicated, a molecule can be loosely thought of as a group of atoms stuck together; usually through chemical bonds.
Let’s imagine a single hydrogen atom traveling through the cosmos; its made of one positively charged proton in its nucleus and one negatively charged electron; if our lone hydrogen atom happens to pass close enough to another isolated hydrogen atom; their electron, which attracted like magnets to proton; can pull the particles towards each other until they collide and stick together. The atoms now share each other’s electrons in what is called a covalent chemical bond. What was once two individual hydrogen atoms have now formed a single hydrogen molecule.This bond is not permanent with enough heat or due to interaction with other molecules; the hydrogen atom will readily separate one more.
Covalent chemical bond: The sharing of electron pairs between atoms.
Different types of atoms can form different numbers of covalent bonds:
A hydrogen atom can form only one covalent bond at a time; if a third hydrogen atom were to collide with a hydrogen molecule, it would simply bounce off, or if it hits just in the right place with sufficient force; it can switch spots with one of the existing atoms. An oxygen atom can typically form two covalent bonds. A carbon atom can make four bonds. An argon atom usually doesn’t bond with anything.
Even though possible bond numbers per atom are pretty small, giant molecules can form if bonds happen to be appropriately arranged. As we can see, a single molecule of sugar known as glucose is made of 24 atoms, a unique arrangement of carbons, hydrogens, and oxygens. Similarly, in the human body, a typical fatty acid may vary in length. And finally, a single protein depending on the type can contain over half a million atoms, all covalently bound together, primarily carbon, hydrogen, nitrogen, and oxygen.
Structure of a molecules:
When we look at real molecules with a scanning tunneling microscope; it looks pretty similar to Space-filling models
But in reality, the atoms are not coloured, and their edges are distorted
When looking at complex molecules, space-filling models and especially actual images of natural molecules can be a bit confusing, which atoms are bound together and which particles are close. That blur is partly due to microscopes limitations and partly because atoms have soft boundaries. For this reason, chemists sometimes use a ball and stick model.
These highlights the bonds between atoms and the skeletal of a molecule instead of showing each atom outside the surface. In 2009 Dr. Leo gross and his team at IBM discovered a way to take actual bony pictures of molecules
Amazingly atomic theory allowed scientists to draw molecules with surprising accuracy over 100 years before this image was finally taken. That’s quite a testament to what good scientific approach can do.
How a molecule behaves:
When atoms come together to form a molecule; the molecule vibrates between its bond in a regular pattern; you can think of bound as a bouncing spring; this is because the protons and the nucleus of each atom repel one another; While the shared electrons in each bond pull the particles back together; the vibrations we find in molecules are the result of an everlasting tug-of-war between these two forces. If you add more energy to a molecule with heat or light, the amplitude and the length of each vibration will increase without changing how frequently each pulse completes its cycle. This means the bouncing spring stretches further, and the atom moves faster; if you add enough energy, the bond will eventually break.