Group 7 & Group 0 (Halogens & Noble Gases)

 Halogens are very dangerous, these are the Halogens:

Florine is a poisonous yellow gas and is very reactive.

Chlorine is less reactive than fluorine but is a poisonous green gas.

Bromine is a dark brown liquid, once again the odour and liquid are poisonous, and the vapour that it creates is heavy, so you can pour out its vapour from a glass ampule

Iodine is a dark purple solid that forms poisonous purple vapours, but it is also a commonly used antiseptic in medical applications. 

Tennessine.

Atatine.

But we will mainly talk about the elements starting from Florine to Iodine, but the elements Tennnessine and Atatine are still important to remember.

All halogens exist as pairs of atoms, referred to as diatomic molecules. This term indicates that these molecules consist of two atoms. They form these pairs by sharing electrons through covalent bonds. Additionally, halogens can bond with other non-metals, such as carbon or hydrogen, using the same covalent bonding mechanism.
Chlorine bonding with Carbon can get you Carbon Tetrachloride.

Unlike the Alkali metals, the Halogens increase their boiling and melting points the further down you go on the chart.
Along with the boiling points increasing, the reactivity decreases, making the elements less reactive.

The reason why they become less reactive is because the electrons get further from the positive nucleus.

When Halogen ionic bonds with metals and collects an electron to become a minus -1 electron, we call those Halides, so we change the 'ne' at the ends of the names of the Halogens so when Bromine bonds with a metal it becomes Bromide, Iodine becomes Iodide, Chlorine becomes Chloride, and Fluorine becomes Fluoride.

Most of the time they bond with the Alkali metals, an example is Sodium Chloride, the Sodium is an alkali metal while the Chloride is a Halogen.

Another thing that Halogens do is that they do something called 'Displacement Reactions', which means that the more reactive Halogen displace the less reactive ones.

So if we pumped some Chlorine gas into a solution of Potsassium Bromide, so the chemical numbers would be Cl(g) + 2kBr(aq), so since the Chlorine is more reactive than the Bromine it will displace the Bromine causing the element to become 2kCl(aq).

Something to keep in mind is that more reactive Halogens will always displace less reactive ones.

 

Surface Area to Volume Ratio

If we take a look at smaller organisms, something to take notice of is that they can use diffusion to exchange substances with their environments.
If we look at humans, we need specialised systems for transport via the heart and blood vessels, like our intestines and lungs for breathing and expelling waste.

The single-celled organisms have to constantly be doing chemical reactions to survive, like gathering amino acids, glucose and Oxygen, and getting waste like carbon dioxide out.

Everything has a Surface area to Volume ratio, for example, a cell has a higher surface area to volume ratio than a cow, as when organisms increase in size, the surface area to volume ratio decreases.

Now calculating this kind of thing is a bit confusing for organisms, instead we will use a small 1cm by 1cm by 1cm cube.

To calculate the surface area, you must first get the length and the width of one face, and multiply them together, so 1cm*1cm is 1cm^2 or 1cm squared, then you multiply it by 6 because a cube is six-sided, to get 6cm^2.
To get the volume of the cube, you need to multiply three values, which in this case is 1cm*1cm*1cm, to get 1cm^3, or 1cm cubed.
So at the end it has a ratio of 6:1, because it is six times bigger than the volume of the cube.

Now if we take another cube and instead of it being 1cm*1cm*1cm, it is 2cm, first we take one face of the cube and multiply it by its height and width (2cm*2cm), then which gives us 2cm^2, then we multiply it by six because six-sided cube then we get 24.

Then the volume is 8, by multiplying all the values 2cm*2cm*2cm, giving us 8cm^3 or 8cm cubed, so putting it into an equation would give a ratio of 24:8, which we can simplify by dividing both equations by 8, which gives us a ratio of 3:1.

The Indus River Valley civilizations

The early civilization came from the river valleys, known as the Harappans, this civilization was in the area of modern-day Pakistan in the Indus Valley, dating as far back as 7,000 BCE.

Around 3,300 to 2,000 BCE, the early Indus Civilization appeared, and that's when the Acadians and the Sumerians began interacting, and then around the 3rd millennium was when the empire of Sargon the Great was established.

Then around the mature period, which is around 2600 BCE, is where most of the advanced structures were found, and if we go to Egypt, around 2500 BCE is roughly when the Pyramids were built.

Then around 1600 BCE is considered the late Indus valley civilization, which is where the Babylonian empire was founded

The Punjab region in Pakistan is where most of our archaeological dig sites are about the Indus Valley Civilization, found around Harappa, which is why it is known as the Harappan civilization too, the largest site is Mohenjo-Daro in the Sindh region.
We believe that over 40,000 people was living in that region alone, with around Harappa and Mohenjo-Daro, there are over 1000 sites scattered all around both regions.

The reason why we think that this is a civilization is because of the sheer size of it all, the standardization of measurement and weight, we have found them using aa measurement of 1.6mm which is precise, we can speculate that there was some cultural interchange, sin they were using bricks that were a standard size so measurements were needed.

In Mohenjo-Daro, we found some sites that these people lived in, from citadels, to public baths, and what was impressive is that we found sewerage systems for carrying waste, along with houses with wells.
Their jewelry is intricate and complicated with shells gathered from the Arabian Peninsula, and the type of jewelry was not only found at these sites but also found in Mesopotamia too, and we speculate that there were probably ships transporting cargo from Mesopotamia and the now modern-day Mohenjo-Daro region. 
Materials from what is now modern-day China and India, they also had their own writing system and they also made Symbols along with a wee known symbol of a Nazi Swastikas', before Hitler used in in his campaigns it is a common symbol in Hinduism, often meaning good luck,.
But we don't really know much about them, other than the stuff we found at dig sites, and since we can't decipher their writing.

One of the strangest things about the Indus Valley Civilization is 'why did it end', they seemed to be thriving with good ties and imports from other civilizations, some ideas on why it ended were maybe they were invaded, some other theories are that it was because of climate change .

As one of the earliest civilizations on earth with a speculation of their whole population maybe reaching  

Components

Components are used in circuits for electricity to flow, and we write these components via symbols.

Firstly, we write multiple vertical lines to depict a Cell or Battery, which powers the circuit.

Wires are written as lines and normally straight, and they carry the current throughout the circuit.

A Fuse is a rectangle with a wire running through it. Its purpose is to prevent the device from being overloaded. When too much power flows through the circuit, the fuse breaks, cutting power.

For switches, it will look like two circles connected via a short line between them, when the line is connected it means the current can flow, but when the switch's line isn't it means the current can't flow.

Then a Diode is a component that only allows current to flow a certain way, a form of diode is a Light Admitting Diode or LED, which lights up when electricity flows through it.

Now, for measuring current, we have Ammeters, which are put in series or connected through the circuit, and Volumeters, which are used for measuring potential difference and are  added in parallel, usually outside the circuit.

Lastly, we have resistors, which 'resist' the current to a specified amount, certain components can only function at certain amounts of electricity, if we put too much power into a component it might fry the circuits and the components might smoke or catch on fire, for example, when you charge your phone, it has resistors in the plug to not take too much power so that the internals don't fry.
Along with normal basic resistors, there are also variable resistors that can be modified so that they resist more or less current based on the situation.

Light-dependent resistors use light as a way of varying the amount of resistance, if you put them in a bright environment will resist a lot less than in a dark one as the darker it gets the more they will resist an application many people use these LDR's is in automatic nightlights which turn on when the lights in the room are off.

Thermistors use heat to vary the resistance so the more heat the less resistant the resistor becomes, and the colder it gets the more resistant it becomes.