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Chemical Bonding Introduction: Hydrogen Molecule, Covalent Bond & Noble Gases

remember we said that it's rare to find

one kind of atom all on its own true it

sometimes happens and when it does we

call that stuff an element like the

carbon in your pencil but most atoms

stick to other types of atoms somehow

they usually like sticking to their own

kind too

this video shows how they can do that

we'll start with the oldest and simplest

kind of atom hydrogen made of one

positively charged proton and one

negatively charged electron

the electron moves amazingly fast around

the nucleus why then doesn't it whiz off

into space

well what kind of force with the

electron and proton field towards each

other attraction or repulsion

I hope you said attraction because they

are oppositely charged it's this force

that bends them into moving in a circle

around the proton it's why atoms don't

fall apart

also an atom is three-dimensional which

means that the electron really whizzes

around in the shape of a sphere not a

flat circle atoms are more like marbles

than coins but here we will simplify the

picture and show the electron in a

circle and not moving

now the main question we're asking is

what happens when two hydrogen atoms

come together

let's bring another hydrogen atom onto

the stage and see what happens

will they bounce off each other and stay

separate we'll stick together

let's take a closer look at the

electrons and protons

what happens when the electron from

hydrogen atom one gets near the proton

of hydrogen atom two electron one and

proton two don't care if they belong to

different atoms they will still be

attracted

and here's the thing the shell of atom 2

is not full it can take up to two

electrons it has the space to allow the

electron from atom 1 to visit it

the same deal happens between the

electron from atom to and the proton

from atom 1

this means that both electrons wrap

themselves around both atoms and they

act as a kind of glue to hold them

together the two atoms become one

molecule

because the shells are partially empty

they can overlap and merge and the

shared electrons then spend more of

their time between the two nuclei

because the nuclei are both attracted to

both electrons between them the atoms

stick together as a stable molecule this

joining caused by atoms sharing their

electrons is called a covalent bond

is there a shorthand way of writing a

hydrogen molecule

scientists sometimes write a covalent

bond as a stick between the two atoms to

show that they are joined

this way of writing is called a

structural formula

they could show it even more simply as

h-h to show that the two hydrogen atoms

move around in pairs

even simpler they could write it as h2

with the two standing for the number of

hydrogen atoms joined by the bond

the two is written as a subscript that

is a little too a bit below the hydrogen

symbol

this way of writing a hydrogen molecule

is called a molecular formula or just

formula

now let's see if helium can bond with

itself like hydrogen can helium atomic

number two is made of two protons and

two electrons when we bring two helium

atoms together we find a big difference

compared to hydrogen atoms

can you tell what it is

the electrons from helium atom one can't

get into the shell of helium atom two

why not

because helium's electron shells are

already full that means that helium

atoms can't share their electrons helium

atom twos electrons can't get into

helium atom one's shell either and this

has the effect that a bond cannot form

between them

in fact because their electron shells

are full they can't share electrons with

any other types of atoms at all helium

atoms are always on their own

we say that their monatomic meaning that

they are always found as just one atom

this is also why helium is always

written as just HD we could put a 1 in

the formula but scientists agree that we

can leave the number out when there is

just one atom and it's not needed

we should feel sorry for helium well

maybe we should admire it because it

doesn't need any other atoms that's why

it's called a noble gas

in our next video we will look at how

oxygen nitrogen and carbon bond with

other atoms