Я нечаянно сломал карандаш и взял другой.

Сломал is the past tense form of сломать (to break).

In Russian, past tense verbs usually show:

• gender in the singular
• number in the plural

So:

• сломал = a male speaker / masculine subject
• сломала = a female speaker
• сломало = neuter
• сломали = plural

Since the sentence begins with Я, we understand it as I broke. The form сломал tells us the speaker is male.

It would be:

Я нечаянно сломала карандаш и взяла другой.

Both past tense verbs change:

• сломал → сломала
• взял → взяла

That is because Russian past tense agrees in gender with the subject when the subject is singular.

Нечаянно means accidentally, by accident, or unintentionally.

In this sentence, it tells us that the pencil was broken not on purpose.

It functions like an adverb:

• Я нечаянно сломал карандаш = I accidentally broke the pencil/a pencil

A learner may also see случайно, which can often mean something similar. In many everyday contexts, нечаянно and случайно are close in meaning, though нечаянно often emphasizes not intending to do it.

Russian uses aspect, and here both verbs are perfective because they describe completed actions.

• сломал = broke / ended up breaking
• взял = took / picked up

The sentence presents two finished events:

1. he accidentally broke the pencil
2. he took another one

If you used imperfective verbs instead, the meaning would shift toward process, repetition, or background action rather than completed results.

For example:

• ломал would sound like was breaking / used to break
• брал would sound like was taking / used to take

So the perfective forms fit the simple completed sequence of events.

Карандаш is in the accusative case, because it is the direct object of сломал.

The verb сломать takes a direct object:

• сломать что? = to break what?
• карандаш

However, for many masculine inanimate nouns, the accusative singular looks exactly like the nominative singular.

So:

• nominative: карандаш
• accusative: карандаш

That is why the form does not change.

Here другой stands for another one and is also in the accusative singular masculine inanimate.

It agrees with an implied noun:

• другой (карандаш) = another pencil

Because карандаш is masculine and inanimate, the accusative singular form looks like the nominative:

• nominative: другой
• accusative masculine inanimate: другой

If it referred to an animate masculine noun, you would often get a different accusative form.

Russian often omits a noun when it is obvious from context.

So:

• взял другой literally means took another
• but naturally it means took another pencil

English usually needs one here:

• I took another one

Russian can use the adjective by itself, as long as the noun is easy to understand from the previous context.

It could be omitted:

Нечаянно сломал карандаш и взял другой.

Russian often leaves out personal pronouns when the verb form already makes the subject clear.

Here:

• сломал
• взял

both show a masculine singular past subject, and the context would usually make it clear that the subject is I.

However, Я may still be included:

• for clarity
• for emphasis
• because it sounds natural in the situation

So both versions are possible.

Yes, Russian word order is fairly flexible.

This version is neutral and natural:

• Я нечаянно сломал карандаш и взял другой.

But other orders are possible, depending on emphasis:

• Нечаянно я сломал карандаш и взял другой.
• Карандаш я нечаянно сломал и взял другой.

The basic meaning stays the same, but the focus changes slightly.

For learners, the given order is a good standard pattern:

• subject
• adverb
• verb
• object
• conjunction
• verb
• object

Yes, и means and.

Here it connects two actions done by the same person:

• сломал карандаш
• взял другой

It gives a simple sequence:

1. broke the pencil
2. took another one

Russian often uses и exactly like English and in this kind of sentence.

Russian has no articles like a/an or the.

So карандаш can mean:

• a pencil
• the pencil

The exact meaning depends on context.

Likewise, другой can mean:

• another
• the other, in some contexts

In this sentence, English would most naturally say:

• I accidentally broke the pencil and took another one or
• I accidentally broke a pencil and took another one

Russian does not mark that difference with articles.

Другой means another or a different one.

Второй means second.

So in this sentence:

• взял другой = took another one / a different one

If you said взял второй, that would sound like:

• took the second one

That suggests a numbered or ordered set, not simply a replacement pencil.

So другой is the correct choice here.

Yes. As an adverb, нечаянно has some freedom of position.

Possible versions include:

• Я нечаянно сломал карандаш и взял другой.
• Я сломал карандаш нечаянно и взял другой.
• Нечаянно я сломал карандаш и взял другой.

The first version is the most neutral and natural for many learners.

Changing the position usually changes emphasis more than meaning. Russian often puts adverbs before the verb in a neutral sentence, which is what happens here.