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Quarter 2 Competency 5 | How Chemistry Was Shaped | MATATAG Science Grade 8
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The periodic table didn’t just appear on our desks
fully formed. Definitely not —
It’s the result of centuries of chemists
organizing, guessing,
debating, and maybe
being just a little extra. Let’s meet the scientists
who shaped the ultimate cheat sheet of chemistry.
Let’s go back o the year 1789…
Meet Antoine Lavoisier — often called the…
“Father of Modern Chemistry.” Before him,
the world of elements was kind of a mess.
People had all sorts of ideas about what ‘stuff’ was made of...
but not many rules. Then came Lavoisier, with a question:
What if we listed all the elements we know…
and grouped them by wha t they have in common?
So in his book Elementary Treatise of Chemistry,”
he listed 33 elements — which, at the time,
was already impressive. And instead of tossing them all together,
he sorted them into metals, non-metals,
gases, and earths.
Now, was it perfect? Not really.
It was basic… But it was a start.
Fast forward a few decades… Chemists started noticing
some strange patterns.” Enter a German chemist
named Johann Döbereiner — who spotted something
that made people raise their eyebrows...”
So, Döbereiner — he wasn’t trying to change the world.
He was just… curious. He noticed something odd
with certain elements. They seemed to come
in groups of three — what he called triads.
Not just random threes… but elements
that looked alike, reacted similarly,
and even had a cool math trick
behind them. Here’s how it worked:
Take the alkali metal triad — lithium, sodium, and potassium.
If you take the atomic mass of lithium and potassium,
and find the average… You get something close
to the atomic mass of sodium — the middle element.
He found this pattern in other triads too —
like the alkaline earth metals, halogens,
and chalcogens. It was like nature
was dropping hints — ‘Hey, these elements are kind of related!’
But … of course… not everyone was convinced.
First of all — there just weren’t enough triads.
Sure, some groups worked — like chlorine, bromine, and iodine...
or calcium, strontium, and barium. But most elements?
They didn’t fit into these tidy little sets of three.”
And scientists? They weren’t looking for a
‘sometimes it works’ kind of system. They wanted something
universal — a pattern that all elements
could follow. Second problem?
Döbereiner couldn’t really explain why it worked.
Why did the atomic masses average out like that?
Why were those three elements so similar?
He had the pattern… but no theory behind it.
So in the end, it was more like a
fun observation than a full
scientific breakthrough. Alright — fast forward again,
this time to 1864.
A chemist named John Newlands
was flipping through the list of known elements...
...trying to make sense of them. And suddenly… something clicked.
Something musical. He noticed that
if arranged from lightest to heaviest,
every eighth element
seemed to share similar properties with the first one.
Kind of like... a repeating tune. So, he called this idea
the Law of Octaves —” Yup,
just like the musical scale: do, re, mi, fa, so, la, ti... do
Let’s try it with this part of his table —
Start with lithium… then move forward,
one element at a time, like a musical scale.
And we land on Na,
or sodium — which, surprise!
acts a lot like lithium. Same goes for beryllium,
magnesium, and calcium.
Every eighth element kind of ‘rhymed’
with the one before. But not everyone thought it sounded great.
Scientists? First off,
they thought it was way too musical for science.
It just didn’t sound serious enough for the scientific crowd.
Then there was the problem with heavier elements.
His pattern worked for the lighter ones, like lithium, sodium,
and potassium... But once he reached the heavier elements —
like beyond calcium — the ‘tune’ got pretty off-key.
It just didn’t fit as neatly as he hoped.
And speaking of fitting… Newlands was so eager
to make his theory work, he squeezed in elements
that didn’t really belong. There wasn’t even room
for future discoveries. No empty spots
for elements that hadn’t been discovered yet. He was on the right track…
but the world of science wasn’t quite ready for his rhythm yet.
Now, after Newlands hit a few wrong notes…
it was time for someone And that person
was Dmitri Mendeleev. In 1869…
Mendeleev decided to throw a little order into the chaos.
Instead of relying on musical patterns, he organized the elements
by atomic mass. He also grouped elements
by similar properties. But here’s the kicker…
He didn’t just organize what was known he predicted missing elements!
For this reason, many call him
the Father of the Periodic Table.
And hey, element 101? Mendelevium.
Named after him — proving just how influential
his work really was. Here’s a portion of Mendeleev’s
Periodic Table. It might look a bit different
from what we’re used to today… but this was the start of something huge.
You’ll notice he arranged the elements
in rows and columns. The columns are called groups —
and there are 8 main groups in this version. Here are the elements of group 1.
Group 2. Group 3.
And group 8. Each group
contains elements with similar properties — like metals and non-metals.
Mendeleev’s table wasn’t perfect… But here’s where
Mendeleev really blew everyone away. He didn’t just organize the elements
he had — he predicted the ones
that were missing! He left blank spaces in his table,
confidently labeling them with names like…
eka-boron, eka-aluminum,
eka-silicon, and eka-manganese.
‘Eka’ was his way of saying… ‘This element
should behave like the one before it in the table.’
And guess what? The missing elements he predicted?
They were eventually discovered — and they turned out to be…
Scandium, Gallium,
Germanium, and Technetium.
He wasn’t just guessing — he had nailed their properties
and placement! Now here’s something really interesting...
Mendeleev said elements should be arranged by
increasing atomic mass, right? From lightest to heaviest.
But then… take a look at this: Iodine,
actually has a lower atomic mass than tellurium.
But Mendeleev put iodine after tellurium anyway. Why?
Because iodine’s properties matched better with the group it landed in.
Same thing happened with cobalt and nickel.
Cobalt has a slightly higher atomic mass, but Mendeleev placed it
before nickel. Again — just to keep the similar properties
lined up in the right group. So even though he valued atomic mass…
Mendeleev chose chemical behavior over the numbers.
And honestly? That idea
turned out to be a genius decision — It showed he understood the bigger picture,
even if the science wasn’t fully there yet.
But there were still a few puzzle pieces that didn’t quite fit.
Why did some elements break the atomic mass rule?
What was the real order hiding beneath it all?
That’s where a young scientist named Henry Moseley steps in.
In 1913, British scientist Henry Moseley.
began using X-ray experiments to study the elements more deeply.
And what he found? It changed everything.
Instead of organizing elements by atomic mass like Mendeleev,
Moseley discovered the real key: atomic number —
That’s the number of protons in an atom’s nucleus.
When he rearranged the periodic table based on increasing atomic number,
Suddenly, all the strange mismatches disappeared —
Everything just… fit. This led
to what we now call the Modern Periodic Law:
‘The properties of elements are periodic functions
of their atomic numbers.’ In simpler terms?
When you line up the elements by atomic number, their chemical behavior
starts to repeat in a predictable pattern.
It’s like a rhythm — same notes,
different octave. Sadly, Moseley’s story was cut short.
In 1914, he joined the British
army during World War I. And in 1915,
he passed away in battle… He was only 27 years old.
It was a tragic loss — especially for the scientific community.
Moseley didn’t just reorder the table — he helped confirm and complete it.
First, his atomic number experiments confirmed the existence of missing elements
like 43 and 61 — which would later be discovered
as Technetium and Promethium. Then, he even predicted elements 72 and 75,
proving the table still had room to grow —
but only in the right places And here’s the best part:
Moseley showed that from elements 13 to 79,
there were no more gaps. No missing pieces.
No mysteries. With atomic numbers as the guide,
everything finally made sense. This marked the end
of the guessing game. Thanks to Moseley,
the periodic table finally had order, logic, and rhythm.
And Just when you thought the periodic table was done evolving…
Enter Glenn Seaborg, in 1945 — this scientist gave us
the modern table. The one we know today.
He noticed something odd about the elements with atomic numbers 89 to 103.
They didn’t quite fit into the main table — their properties were unusual
compared to the others. So instead of forcing them into place,
he pulled them out into a separate row.
But Seaborg didn’t stop there
Between the 1940s and 1950s, he discovered plutonium
and co-discovered other super-heavy elements beyond uranium.
And get this — in 1980, he actually turned bismuth into gold.
Not practical…
but scientifically? He made it happen.
And in 1997, Glenn Seaborg got one
of the rarest honors in science — Element 106
was named seaborgium… while he was still alive.
That. Never. Happens. It was like
the periodic table tipped its hat to him. Before Seaborg,
the periodic table looked… a bit cramped.
The f-block elements — the lanthanides and actinides —
were squeezed into the main body like puzzle pieces that didn’t quite fit.
It worked... sort of. But it made the table feel crowded
and confusing to interpret. So Seaborg had an idea:
pull them out — and give them space to breathe.
and just like that — the modern periodic table
as we know it was born.
It wasn’t just a small design change —
It was a major step in organizing the building blocks of matter.
So the table we use today? It’s not just a chart —
it’s a collection of stories. And Seaborg’s chapter helped
shape the final look. From curious patterns…
to triads and tunes… to bold predictions
and powerful experiments — the periodic table didn’t appear overnight.
It was built slowly, layer by layer,
by scientists who asked the right questions — and sometimes,
the weird ones. They didn’t always get it right.
Some were laughed at, others were ignored.
But each one moved us a little closer
to the beautiful order hidden in the elements.
And today, we don’t just use
the periodic table — we understand it.
We teach it, test it, expand it… and keep it growing.
Because chemistry isn’t just about memorizing symbols.
It’s about discovery. It’s about patterns.
And it’s about people bold enough to look at the unknown —
and say, “Let’s figure this out.”
This is Learning with G — see you in the next one.
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